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This paper discusses the time lag in brushless DC motor system, which leads to increase system dynamic error, decrease stability margin and affect the system stability. Based on the Smith compensation control theory, the predictor of time lag is designed. However, an accurate and stable mathematical model is needed for traditional Smith predictor to get satisfactory control quality. If not, it may lead to divergence and oscillation easily. In this paper a modified Smith predictor is proposed, which use fuzzy-PI controller to eliminate the parameters' deviations between Smith predictor and actual control object rapidly. So it ensures that the state of the system is steady. This scheme enhances robustness of the controlled system and alleviates the disadvantage of traditional Smith predictor in which an exactly precise model is needed. Simulation results show that the proposed method has good parametric adaptability and can improve the performance of brushless DC motor system with time-varying parameters and time lag.