Constant current regulator (CCR) is to provide visual guidance for aircraft taking off and landing. The detection of the lamp fault is very important function of CCR． The international standards and national standards are strict requirements on the functionality, but the principles are not discussed. This subject was discussed in the article, using the BP network to monitor the circuit failure as well as to estimate the number of the fault light . Practice shows that way introduced in this article can monitor the circuit failure effectively and report the number of fault lights accurately.