The Structure of Radar Side-Lobe Cancellation (SLC) System is determined by its capability measurement rule and the corresponding algorithm, SLC is one of the key techniques in the enhancement of radar electronic war capability. To improve the convergence speed and stable state capability of the algorithm in radar SLC, an improved un-constant-step LMS algorithm based on S-function is put forward aimed at the general problems (low convergence speed and poor stability) existing in the un-constant-step LMS algorithm. The simulation results show that this system can fast restrain the jamming, effectively improve the system Real-time and stable state capability. And the experimental verification is done based on the requirements of the real application circumstances, the result shows that: when two coherent jamming source and the inner noise of receiver are in existence, the application effect of double CSLC is better than that of single CSLC.