To realize the long-time dynamic stability for the tiled-grating control system,a PID algorithm based on the analysis of the four-dimensional degree of freedom mathematical model for the tiled-grating is developed. Two improvements are made in incremental PID algorithm. The latches compensation method is used to avoid saturated loss,and the four-point center difference method is applied to avoid interference. The splicing spot photos of the tiled-grating’s closed-loop control experiments demonstrate that the tiled-grating which employs the improved PID algorithm can acquire a long-time stability as well as the stability can keep one hour.