To solve the fault diagnosis problem of liquid propellant rocket engine ground testing bed, a fault diagnosis approach based on self-organizing map (SOM) is proposed. The SOM projects the multidimensional ground testing bed data into a two-dimensional map. Visualization of the SOM is used to cluster the ground testing bed data. The out map of the SOM is divided to several regions. Each region is represented for one fault mode. The fault mode of testing data is determined according to the region of their labels belonged to. The method is evaluated using the testing data of a liquid-propellant rocket engine ground testing bed with sixteen fault states. The results show that it is a reliable and effective method for fault diagnosis with good visualization property.