The invention provides a vehicle-borne platform supporting leg synchronous control method and system. A vehicle-borne platform comprises a main controller and supporting legs. Each supporting leg is provided with a multi-way valve and a displacement sensor. The control method includes the steps that when the supporting legs start to act, the main controller transmits controlled quantities to the multi-way valves, and the multi-way valves control the supporting legs to move according to initial planning speeds of the same numerical value; in the acting process of the supporting legs, the displacement sensors collect supporting leg actual signals of the supporting legs corresponding to the displacement sensors in real time, and transmit the supporting leg actual signals to the main controller; and the main controller transmits the controlled quantities to the multi-way valves corresponding to the controlled quantities after correcting the controlled quantities of the other supporting legs with the actual signal of any supporting leg as the reference, and the multi-way valves control the supporting legs to move synchronously. By means of the vehicle-borne platform supporting leg synchronous control system, synchronous stretch-out of the vehicle-borne platform supporting legs can be achieved. By means of the vehicle-borne platform supporting leg synchronous control method, synchronous stretch-out of the vehicle-borne platform supporting legs can be achieved.