The invention relates to a histone methyltransferase EZH2 inhibitor, a preparation method and pharmaceutical use thereof. In particular, the invention relates to a compound represented by the general formula (I), a preparation method thereof, a pharmaceutical composition containing the same, and a use thereof as a histone methyltransferase EZH2 inhibitor for treating diseases associated with the histone methyltransferase EZH2, especially cancer. The definition of each substituents in the general formula (I) is same as the definition in the specification.
