The invention relates to an overload protection device of a gear case for a slurry pump. The overload protection device comprises a clutch at an input end of the gear case; the overload protection device is characterized in that a rotating speed sensor is arranged on a driving shaft of a mainframe; the rotating speed sensor controls the working state of the clutch by a controller through a hydraulic valve; when the rotating speed is lower than 85% of rated rotating speed, the clutch is automatically opened and then the rotating speed of the driving shaft of the mainframe quickly rises to the rated rotating speed again; and the clutch can be closed to work after being delayed for at least 30s.