STAP greatly enhances the degree of freedom without increasing the number of array elements, at the same time, the high computational complexity becomes the main obstacle in its engineering implementation. Reduced-dimension processing to the receiving data has becomes the main method of resolution. Under the background of GPS receiver joint space-time interference, the performances of reduced-dimension method are analyzed and simulated in this paper, the result shows that the reduced-rank multistage Wiener filter(RR-MWF) based reduction-dimension technique outperforms other traditional methods, it dramatically reduces the amount of computation in GPS space-time interference and has a better convergence and interference performance.