Abstract: In order to investigate a digital modulation applicable for underwater wireless optical communication (UWOC), the model of the UWOC channel was analyzed. The packet error rate, bandwidth efficiency and energy efficiency of the channel based on multilevel digital pulse interval modulation (MDPIM) was deduced. Comparison was carried out between different modulation modes. Both power efficiency and bandwidth efficiency are the highest for MDPIM. The results help to determine the modulation suitable for underwater wireless optical communication.