The invention discloses an automatic test system for onboard cable integrity. The automatic test system comprises a test host and multiple test terminals, wherein the test host and the test terminals are connected through a CAN bus network, and the test terminals are distributed at the portions needing to be tested of an airplane. Each test terminal comprises a CAN bus input interface, a CAN bus node processor, a cable test extension box, a switch board, an analog bus and a digital bus. The test host gives out a control command, after the test terminals receive the command through the CAN, relays on the switch boards are controlled to be switched on, thus, a test loop of a cable is formed, and a function test is finished. Through the technology of CAN application, database drive and the like, the automatic test system has the advantages of being high in test speed and accuracy, capable of reducing the length of the switching cable and the like.