The invention discloses a precision machining method based on a PLC integrated control system. The PLC integrated control system is provided with at least two molding machines. A data processing control module of the PLC integrated control system carries out calculation by combining the received data information of a semi-finished product manufactured by a previous molding device and design requirements to obtain optimum forming temperature, pressure and displacement parameters, converts the parameters into action control instructions which can be executed by a manufacturing machine, and transmits the action control instructions to a communication module, a distributed digital quantity input and output module and the manufacturing machine in sequence to control product manufacture. The method can realize simultaneous on-line monitoring of process parameters and status information of forming equipment on a production line, can carry out intelligent optimization processing on the data based on a historical high-quality product qualification database, and then, carry out intelligent control according to the optimized parameters, thereby improving manufacture efficiency and secondary manufacture precision and meeting market demands of clients.