Artificial neural networks (ANN) are an information-processing method of a simulation of the structure for biological neurons.C3I system as a modern combat unit can control and command the army action and can communicate to others.This paper makes a research on the approach of the artificial neural network for fault diagnosis of CsI system and constructs a fault diagnosis system of C3I system with ANN.And the system can analyze fault phenomena and detect C3I system fault.It will greatly improve the response to the C3I system fault diagnosis and maintenance efficiency.