To solve the quality risk in simultaneous machining of large aircraft parts by using multiple CNC machine tools, based on the fast I/O function of the Siemens 840D SL system, a multimachine tool electrical and program cooperative control method was proposed. By using the method, the parallel interlock function of multiple devices can be realized, which effectively solves the problem of processing quality risk existing in the simultaneous movement of multiple devices and provides reference for the digital processing of large aircraft components.