In order to meet the requirements of underwater high-speed laser communication and improve the error code performance of the system, an underwater high-speed laser communication system based on on-off keying(OOK) modulation is designed. The sliding window average filtering method is used to denoise the received data, and the threshold decision is made after the joint threshold is obtained according to the fixed threshold and the adaptive threshold. The system test results show that the bit error performance of the joint threshold decision mode is better than that of the fixed threshold decision mode and the adaptive threshold decision mode. The bit error rate of the system is about 0 and 10-2 respectively when communicating with clean water and water containing a small amount of suspended impurities.