Abstract: Deceive jamming is one of jamming methods to SAR. But it is hard to put into practice for big amount of computation. In this paper, deceive jamming algorithm is analyzed and improved. A highly efficient fast algorithm was put forward. Original algorithm calculates signal of each cheat-target and adds them together. Improved algorithm calculates modulated phase first and then get the deceive signal. The improved algorithm cuts computation amount and can be used in real time jamming signal generation. Simulation shows that the algorithm has good performance.