Abstract: A basic mathernatic model of working state for the driving roll system of continuous casting equipment was studied on the collected data. A BP neural network was applied to build the working state model, and the analyzed data was used to train this BP neural network. The even strength value's curve of driving rolls in same time was simulated with the BP model. This BP model was used as casting equipment's conk outs diagnosing model in the expert system for continuous casting driving roll system's computer diagnosis. With the model and algorithm of conk outs judgment, some failure of on-line roll's engine was diagnosed exactly. The bad effects of driving motor troubles on the steel band were avoided.