A system for establishing a center of gravity of a device under test (DUT) includes a test platform and a control device. The test platform includes three support elements and a marker. A sensor is positioned on top of each support element. The control device includes three processing modules and a central processing unit (CPU). Each sensor senses a pressure of the DUT on a support element, and outputs an analog signal to a processing module. Each processing module converts the analog signal into a digital signal, and outputs the digital signal to the CPU. The CPU controls the marker to make a mark on the DUT when values of three digital signals received from the three processing modules are equal.