Liquid crystal spatial light modulator (LC-SLM) can be readily used to fabricate the diffractive optical elements. However, a disadvantage of the finite resolution always exists in LC-SLM. In this paper, a new scheme of fabricating phase grating with LC-SLM is proposed to produce one-dimensional (1D) and two-dimensional (2D) array of optical traps. The advantage of the LC-SLM is fully utilized and the disadvantage is well avoided in our scheme. The phase distribution of the grating is optimized by using iterative Fourier series expansion. The grating is designed by simulation according to the LC-SLM technique parameters, and the corresponding light intensity distribution is calculated. The results show that the array has very high peak value intensity and big gradient of intensity by illuminating the grating with a large detuning and low power laser. The optical dipole potential of trapping cold atoms achieves the order of mK, and the interaction force between atom and optical field is much greater than the atom gravity.