The probability of the target detection must be increased and the intensity of the noise must be decreased in pre－detection because the algorithms based on energy accumulation are sensitive to the misdetection of the target and the intensity of the noise. When the intensity of the noise is larger than three percent, for example, the capability of the detection using high order correlation will decrease rapidly. And when Hough transform is used in target detection in the condition of large noise intensity, not only the calculation would be very heavy but also the capability of detection would be not ideal. Therefore, a self－adaptive threshold pre－detection method using multi－frame indexing accumulation based on energy accumulation is developed.