Fiber coupler is widely used in optical fiber communication, laser detection, electro-optical transmission and other systems because of its many advantages. With the improvement of the performances of optical systems, higher requirements are put forward for the analysis of the influence of fiber coupler on the performances of optical systems. The influence of different input wavelength on the output splitting ratio of 1×2 fiber coupler is researched and analyzed. At the same time, by testing extinction ratio and one hour output power stability of the optical system, the influence of ordinary, polarization maintaining and single polarization 1×2 fiber coupler on the performance of optical system is compared and analyzed. The results can be used to guide the application of fiber coupler in high-performance optical engineering system.