In radar usually the side-lobe blanking system is adopted to eliminate pulse-type interference from side-lobe. But SLB system also results in detection-loss. In order to solve this problem, this paper establishes a model of SLB system, studies the cause of the detection-loss resulting from SLB system, gives the definition for the detection-loss probability and derives the equation of the detection-loss probability based on non-central chi-square distribution. The equation illustrates that the radar detection threshold, antenna gain parameters, blanking threshold, mean SNR all can influence the detection-loss probability. The theoretical analysis and simulation proves that different blanking thresholds will result in different outcomes. At last, fix on an optimum blanking threshold is fixed on to reduce the probability and eliminate interference well, and a simulation is done to verify the importance of the conclusion.