The invention discloses a method for adjusting the mould clamping force. The method comprises the following steps that A, a programmable logic controller (PLC) receives the target mould clamping force F input by a user; B, according to the target mould clamping force F, the PLC calculates the target rotating tooth number N of a corresponding gear; C, the PLC outputs a signal to control a hydraulic motor to rotate and then drives a gear mechanism on a tie bar to rotate, and a movable mould plate is driven to move; D, the PLC receives the current rotating tooth number N', sent by an electromagnetic induction sensor, of the gear; and E, when N'=N, the PLC controls the hydraulic motor to stop rotating, the process is finished, and otherwise, the step C is returned. Through a system, the mould clamping force of a machine hinging type mould closing mechanism can be automatically adjusted, the cost is effectively reduced, meanwhile, the system adopts all-digital signals, the interference or data distorting phenomenon does not occur, and the mould adjusting efficiency is greatly improved.