Abstract: In order to increase the detection distance of the photoelectronic imaging underwater system and decrease its cost, the existing problem in the rangegated technology was analyzed and studied. A novel method for decreasing single pulse energy, enhancing system frequency and lengthening exposure time of charge coupled device (CCD) was proposed. Due to the random feature of the noise and relevance feature of the objective reflencetance, the mutiplue frame accumulation could enhance the maximum distance. The range-gated system was improved by such method, which was checked in the indoor water channel by the experiment. The experimental results show that this method can increase the detection distance effectively, and there is an optimum relation between the image quality and laser pulse numbers which is obtained by 10 pulses at the 29 m distance.