The present disclosure provides an adaptive modulation method for a naive Bayes classifier-based energy harvesting relay system. First, a sending end determines its modulation mode based on a status of a data buffer of a relay, so that sent data does not exceed a storage capability of the relay. Then, based on data sent by the sending end, and channel status information and energy harvesting status information within a period of time, the relay determines an optimal modulation mode used by the relay within the period of time. After that, the modulation mode, the channel status information, and the energy harvesting status information are used as training data to obtain a classification model based on a naive Bayes classifier algorithm. In this way, the relay can adaptively select a modulation mode when only knowing of channel information and energy information in a current timeslot.