In order to improve the reliability of underwater helmet optical wireless communication system,a new (3，1，1）convolutional code is designed.Underwater optical communication model and its requirement for code are introduced,the bit error rate of uncoded system in underwater AWGN channel is calculated.The methods of encoding and decoding are presented;the calculated formula of bit error rate of encoded system is obtained.Both the uncoded system and the encoded system were simulated in different system parameter,water quality and transmission distance.The simulation results indicate that the bigger system parameter,the stronger ability of improving system capability by code;the bigger attenuation or transmission distance,the lower ability of improving system capability by code.