Based on the ideal opening model for the laser resonator and its coherency modal theory in the space-frequency domain, evolution rules of complex spatial coherency of optical fields in the resonator with spatial-phase modulation are investigated by numerical simulations. The physical mechanism of these phenomena is presented and discussed. Results from numerical analyses show that, with increases in the number of reciprocating times of optical fields in the resonator, the complex spatial coherency trends to be completely coherent, while their evolution rules are greatly different for different spatial-phase modulations.