The present invention relates to a benzofuran derivative, a preparation method thereof and a use thereof in medicine. In particular, the present invention relates to the benzofuran derivative as shown by general formula (I), the preparation method thereof, a pharmaceutical composition containing the derivative, and uses thereof as an EZH2 inhibitor and in the prevention and/or treatment of diseases such as tumours and cancers, etc., and in particular uses thereof in the prevention and/or treatment of non-Hodgkin' s lymphoma, diffuse large B-cell lymphoma, follicular lymphoma and synovial sarcoma, wherein the definitions of the substituents in the general formula (I) are the same as those defined in the description.