The dual-step dual-team holographic method to fabricate square lattices is proposed. The effect of intensity threshold was analyzed by calculating the intensity spatial distribution. The photonic band gap properties of two-dimensional square lattice fabricated by holographic lithography are investigated numerically. The influences of intensity threshold and dielectric contrast on photonic gap are comprehensively studied by plane wave expansion method. Calculations of band structure as a function of the intensity threshold show that the full photonic band gap does not increase monotonically with dielectric contrast ratio, but has a peak value instead by studying the relation between the complete PBG and the dielectric contrast.