Infrared thermal imaging technique, a new non contact detection method, was introduced into reliability detection and faults diagnosis of spaceborne TWTA and its detection principle was also presented. Then, a new effective model, which basess on methematical statistics and matrix norm theory and uses infrared thermal imaging technique, was put forward for PCB reliability detection. On the basis of the model, a PCB faults diagnosis method, which bases on examples database, was advanced. Finally, applications of the PCB reliability detection model and faults diagnosis method to spaceborne TWTA were presented.