The invention relates to a synchronous control system of a multi-cylinder loading testing machine. The synchronous control system comprises a base, a synchronous control system body and supporting columns arranged at the upper end of the base, and further comprises a beam arranged at the upper ends of the supporting columns. The synchronous control system further comprises a fixed chuck and a movable chuck which are arranged between the base and the beam. A force measuring sensor arranged between the fixed chuck and the base is further included. The synchronous control system further comprises oil cylinder barrels arranged on the side faces of the supporting columns. Pistons penetrating the oil cylinder barrels are further included. According to the synchronous control system of the multi-cylinder loading testing machine, the moving displacement of the pistons is collected through magnetic induced telescopic displacement sensors, the opening amount of servo valves corresponding to oil cylinders is adjusted through the synchronous control system body, the opening amount of the servo valves corresponding to the oil cylinders with the large piston displacement needs to be properly reduced, on the contrary, the opening amount of the servo valves corresponding to the oil cylinders with the small piston displacement needs to be properly increased, and balance can be achieved so as to achieve the purpose of synchronous control.