This paper deeply discusses the cascade control system and the smith - predictor system of the conventional control system , states a combination system between them in order to improve the weaken control quality of the cascade system which involve a negligible large time - delay in its inner loop 本文对常规控制理论中的串级控制和smith预估补偿控制两种控制方案进行了讨论,引出了利用smith预估补偿控制特点来解决串级控制系统的副回路中存在大纯滞后环节时,系统控制品质差的问题。