For model reference adaptive system(MRAS) of induction motor based on rotor flux,it is difficult to get satisfied dynamic performance and identification precision by using normal fixed parameter PI adaptive speed identification arithmetic.In this paper,after analyzing the effects of various parameters in the variable parameters PI speed identification,a new type of variable parameters PI speed identification arithmetic is proposed.Both the theoretical analysis and the experimented results show that the proposed variable parameters PI speed identification has a faster dynamic response and better identification precision than the fixed PI speed identification.