Liquid crystal phased array can be widely used in space laser communication, space laser ranging and other fields. A phased array device is a diffractive optical device, which has the function of dispersion. That is, the incident light of different wavelengths has different exit angles after passing through the phased array device., The central wavelength of the laser usually has a drift with the design value, and the laser also has a certain spectral width, which will lead to changes of the position deviation and the optical power distribution when the laser beam has large angle deflection by the phased array device. To solve this problem, the relationship between the wavelength and the coordinates of combined liquid crystal phased array devices is derived through the dispersion theory about the liquid crystal spatial light modulator and cascaded liquid crystal polarization grating. The optical power distribution formula of Gaussian beam passing through the combined liquid crystal phased array devices is derived by the combination of the optical power spectrum distribution of laser light source and the cross-sectional power distribution formula of the single-mode laser. Arming at the difficulty in formula calculation, a simple calculation method is given. The beam position deviation and the laser cross-section light power distribution of a common example are calculated. In this example, the laser wavelength is 1 064 nm, the center wavelength shift is 0.05 nm, the spectral width is 0.05 nm, the power is 1 W, the emitted light is a Gaussian beam near the basic mode, and the beam divergence angle is 20 μrad. When the beam passes through a cascade polarization grating with a designed deflection angle of (22.5°,-16.25°), the beam coordinate deviation is (26.76 m,-19.60 m) outside 1 000 km, laser beam cross-section presents an approximate elliptical distribution, the optical power distribution diagram is not rotationally symmetrical. The optical energy extends in the dispersion direction, and the system with a receiving aperture of 1.0 m can receive optical power of about 1.9 mW at the center, which is 24% different from that under the condition of uniform optical power distribution. When the beam passes through a cascade polarization grating with a designed deflection angle of (22.5°,-22.5°), the beam coordinate deviation is (30.79 m,-30.79 m) outside 1 000 km, and the light power also extends in the dispersion direction, the system with a receiving aperture of 1.0 m can receive light power of about 1.4 mW at the center, which is 36% different from that under uniform distribution. When the beam passes through a cascade polarization grating with a designed deflection angle of (27.5°,-16.25°), the beam coordinate deviation is (38.23 m,-22.84 m) outside 1 000 km, the system with a receiving aperture of 1.0 m can receive light power of about 0.97 mW at the center, which is 62% different from that under uniform distribution. It can be obtained from the data that the change caused by dispersion increases with the increase of dispersion angle, the center position deviation becomes more serious with the increase of dispersion angle, and the peak position power density decreases with the increase of dispersion angle.