The present invention relates to the field of pharmaceutical chemistry. Specifically, the present invention relates to a series of BET (bromodomain and extra-terminal domain) inhibitors having a novel structure, particularly inhibitors targeting BRD4 (bromodomain-containing protein 4), and a preparation method and use therefor. The structure thereof is shown in the following general formula (I). Said compounds or a stereoisomer, racemate, geometric isomer, tautomer, prodrug, hydrate, solvate, or crystal form thereof, or a pharmaceutically acceptable salt and a pharmaceutical composition thereof can be used for the treatment and/or prevention of related diseases mediated by bromodomain proteins.
