The invention discloses a module testing system in a limit signal computer. The module testing system comprises a control module, a power module, a serial port communication module, a switching value control module, a 429 bus control module and an A/D and D/A conversion control module. The power module, the serial port communication module, the switching value control module, the 429 bus control module and the A/D and D/A conversion control module are all connected with the control module. According to the module testing system, a one-by-one detecting function is achieved, and a basic platform for providing various power sources and excitation for various functional circuit boards is set up. The work state of the product on an airplane is simulated, the accuracy and consistency of data are effectively verified, and the fault point of the product is determined. The testing capacity on a matched plate of the limited signal computer can be achieved, the repairing efficiency and quality are improved, a large amount of cost is reduced, and the circuit boards in better accordance with the actual product work mode can be concurrently tested and popularized.