The invention discloses a specialized pin-mounting device for an M-pin based on an automatic block, and relates to the technical field of electric power maintenance tools. The specialized pin-mountingdevice comprises the automatic block, a pin-mounting unit arranged on the automatic block, a control unit and a driving unit. The driving unit includes a hydraulic rod and movable arm driving motors.The pin-mounting unit includes a U-shaped frame, a sliding plate, a supporting plate, sliding grooves, externally-expanding side plates and movable arms. A start and stop switch of the control unit,a front and rear travel switch of the control unit, externally-expanding side plate proximity switches and movable arm proximity switches are separately connected to the control end of a controller. The control end of the controller is connected to the control end of the automatic block, the control end of the hydraulic rod and the control ends of the movable arm drive motors separately. Through the automatic block, the pin-mounting unit, the control unit and the driving unit, intelligent control is realized and automatic live installation of the strain insulator string M pin is completed, theoperation is convenient and fast, and the use is safe and reliable.