［Purposes］ The purpose of this paper is to solve the common problem of response delay in long time delay control systems and improve the performance of long time delay systems.［Methods］ Based on automatic control theory and feedback control theory, the model of long time delay system is established. Smith predictor is studied in detail, and its internal filter and controller are improved accordingly.［Findings］ The improved Smith predictor can not only shorten the response time of the system with long time delay, but also improve the robustness and disturbance rejection of the whole control system. Compared with other traditional control systems, the new control system has obvious advantages.［Conclusions］ The improved Smith predictor reduces the influence of time delay on the control system and provides a new solution for the control of long time delay systems.