Space gravitational wave detection is a groundbreaking effort to observe spacetime ripples caused by cosmic events. It requires deploying laser interferometry systems with inter-satellite baselines ranging from hundreds of thousands to millions of kilometers. These systems need detect picometer-scale displacements induced by gravitational waves. However, this task faces significant technical challenges. Key challenges include ultra-long interferometric baselines (~1 million kilometers), small telescope apertures (~100 mm), and beam degradation due to space environmental factors such as thermal fluctuations, radiation, and residual gas interactions. These effects lead to substantial laser power attenuation (down to ~100 picowatts at the receiver) and distortions in beam parameters, including wavefront, polarization, and pointing stability. Achieving sub-nanoradian precision in beam pointing control is critical to maintaining phase stability and ensuring a sufficient signal-to-noise ratio. To address these issues, this study introduces an innovative electro-optic beam-pointing control system using lithium niobate (LiNbO₃) crystals. This system is designed for high precision, environmental robustness, and scalability. We analyzed various beam-steering technologies, including non-mechanical methods (e.g., electro-optic, acousto-optic, and liquid crystal) and mechanical methods (e.g., fast steering mirrors and rotating prisms). Our analysis highlighted the limitations of current technologies, particularly in terms of precision, adaptability to space environments, and wavefront preservation. The proposed system leverages the superior electro-optic properties of LiNbO? crystals. These crystals have a high electro-optic coefficient (r₃₃=30.9 pm/V at 632.8 nm, r₃₃=29.49 pm/V at 1 064 nm) and excellent optical transparency in the near-infrared range, making them ideal for high-precision beam steering. The core innovation is in the system's symmetric optical design. It actively compensates for effective thermo-optic effects, a critical bottleneck in conventional devices. By placing paired LiNbO? crystal prisms in an antiparallel alignment of the optical axes, the design cancels out thermally induced refractive index gradients. The effective thermo-optic induced refractive index is about 9.3×10??, smaller than the refractive index gradient of LiNbO?, ensuring stability in the harsh temperature conditions of space. We rigorously evaluated the system's performance through simulations and experiments. Voltage-deflection modeling showed a linear response, with 720 nrad of beam steering at 5 V and a resolution of <1 nrad/mV. These results demonstrate the feasibility of real-time adjustments in dynamic space conditions. Prototype devices were fabricated using ultra-precision diamond turning and optical bonding techniques. They achieved a central clear aperture of 2 mm with minimal wavefront distortion. Zygo interferometric measurements (λ=632.8 nm) showed a transmitted wavefront error of 0.2λ RMS, mainly due to limitations in the optical bonding process and surface roughness. However, the error meets the minimal optical requirements for high-voltage deflection testing. Beam deflection tests using a high-resolution infrared CCD camera measured a maximum angular displacement of 1.88 milliradians (mrad) under a 15 kV driving voltage. This result closely matched theoretical predictions. Other metrics include a deflection sensitivity of 125 μrad/kV, allowing precise control with moderate voltage inputs. The beam profile distribution was nearly Gaussian across the temperature range, ensuring minimal sensitivity degradation. These advancements demonstrate the feasibility of LiNbO?-based electro-optic systems for next-generation gravitational wave observatories like LISA (Laser Interferometer Space Antenna), TianQin, and Taiji. Our work contributes to ground verification platforms for testing million-kilometer-scale laser links, filling critical gaps in system-level testing. Moreover, the design is adaptable to other high-precision applications, including quantum communication terminals requiring sub-μrad beam alignment and deep-space laser ranging systems that need robust performance in varying thermal environments. By solving thermo-optic stability and precision issues, this research accelerates the development of reliable large-scale space interferometry and opens new possibilities for advanced photonic technologies in astrophysics and beyond.