Applying the MMLS3 system, permanent deformation of asphalt mixture was studied at 45℃ under moisture loading action. Compared with the rutting behavior under dry condition, the results are drawn that, the rutting depth is higher under water condition than dry condition, the effects of water is mostly shown in the initial compression phase. The creep slope of specimen under immersion increases, compared to the specimen under dry condition. The deformation ratio between moisture and dry condition follows the power function relationship with the loading number, and decreases with loading number increasing.