The invention discloses an air duct explosion venting device of a coal mill. The air duct explosion venting device comprises an explosion venting cavity (3) and a valve (4), wherein the valve is arranged at a sealing installation position; under the action of gas explosion pressure of an air duct, the valve can move in the explosion venting cavity and get away from the sealing installation position for explosion venting; the valve comprises a valve rod (1); a pre-tightening spring (5) sleeves on the valve rod; a flange plate (12) is formed on the valve rod; one end of the pre-tightening spring is arranged on a shell (2) of the explosion venting cavity, and the other end of the pre-tightening spring leans against the flange plate elastically; the air duct explosion venting device also comprises a magnetic body (11); at the sealing installation position, the flange plate is jointed with the magnetic body by absorption; the inner wall of the shell is provided with a plurality of guide grooves along the moving direction of the valve; a plurality of roller wheels are arranged at the periphery of the valve and respectively slide in the guide grooves in a one-to-one correspondent way. After the air duct explosion venting device is used, the problems of maloperation of a valve opening seat and blocking of a valve return seat can be solved, the safety factor of the air duct explosion venting device is improved, and the air duct explosion venting device is safe and reliable to use.