The invention relates to the technical field of valves, in particular to a butterfly valve with a preliminary pressure relief function. The butterfly valve comprises a valve body, a disc assembly, a valve seat and a preliminary pressure relief mechanism, wherein the disc assembly comprises a rotating shaft, a first disc and a second disc; the rotating shaft is fixedly connected with both the firstdisc and second disc; the valve seat comprises a first valve seat body and a second valve seat body; mounting hole used for the mounting of the first valve seat body and the second valve seat body are correspondingly formed in the two ends, in the axial direction of the rotating shaft, of the valve body; the preliminary pressure relief mechanism comprises a first butterfly plate, a second butterfly plate and a connecting rod assembly; and the connecting rod assembly is used for driving the first butterfly plate and the second butterfly plate to move oppositely or reversely. The butterfly valve provided by the invention has the advantages that when the valve body is converted from the closed state to the open state, part of a fluid at the two ends of the valve body can be circulated by thepreliminary pressure relief mechanism before a handle is pulled by working personnel, thereby balancing the pressure intensity at the two ends of the valve body, reducing the handle pulling torque, and greatly reducing the working difficulty of the working personnel.