The utility model relates to a synchronous control system of a side crane. The synchronous control system comprises a plurality of tilt angle sensors, PID controllers, displays and wireless remote controllers, which are arranged on the front and rear cranes of the side crane, wherein the receivers of the plurality of tilt angle sensors, the PID controllers, the displays and the wireless remote controllers are all connected through a CAN BUS to form a CAN BUS control network; the plurality of tilt angle sensors can be used for providing real-time detected variable-amplitude angle signals of the front and rear cranes for the PID controller through the CAN BUS; the receivers of the wireless remote controllers are used for wirelessly receiving remote control signals emitted by the emitters of the wireless remote controllers; the PID controllers are used for outputting currents for adjusting the opening degrees of proportional solenoid valves to the corresponding proportional solenoid valves of the front and rear cranes according to the remote control signals and the variable-amplitude angle signals to enable the front and rear cranes to synchronously move. According to the synchronous control system, the side crane can run stably during lifting as well as loading and unloading of containers, and the danger caused by tilting of the containers at a larger angle is prevented, so that the working efficiency, the safety and the reliability are improved.