Liquid crystal spatial light modulator (LCSLM) can be applied to beam steering. Considering that the one-dimensional scalar diffraction analytic method can only solve the diffraction efficiency, two-dimensional scalar diffraction numerical method is introduced and the sampling demand and realization algorithms are strictly analyzed. After phase stages and nonlinearity of LCSLM are modeled, the spatial distribution of circular beam through LCSLM and focus lens is calculated, diffraction efficiency and steering accuracy are simulated with variety of parameters. The relations between the stages and accuracy efficiency with different steering angles are concluded, which can provide choosing basis for liquid devices. Using BNS 256×256 liquid device, the beam steering experiment in which the accuracy and efficiency of different steering angles are researched is established and simulations according to experimental parameters are also done. The experimental and simulation results show good agreement, which demonstrates that two-dimensional scalar diffraction can be used for engineering performance evaluation of LCSLM device.