The circuit design of Ethernet’s interface based on MPC8377 and JEM971A is described. The design problem of low signal transmission speed in application is tested and analyzed to find and analyze the fault reasons. The components in application is tested and analyzed. The faults from input and output of the hardware circuit are tested. The writing software is used to test and analyze. Printed board circuit is analyzed and tested to shoot the fault through comparing method. The fault reasons and solutions are found to obtain the correct design conclusion, which provides the valuable application design advices to the designers.