Abstract: With PSU/NCAR nonhydrostatic mesoscale model MMS,the 24 h rainfall during 12 UTC 11-12 UTC 12 July 1994 caused by Typhoon Tim (9406) is simulated in this paper. Scale discreting is performed on the results with filtering scheme. Analyses on the mesoscale fields show that the interaction between typhoon and westerly trough is apparently manifested by mesoscale activities. The distribution of divergence fields at lower and upper levels can have a kind of indication meaning for the rainfall caused by the interaction between mid and low latitude circulations. Furthermore,intensity changes of westerly trough would directly lead to intensity changes of mesoscale systems and thus lead to different rainfall.Besides,energy change features of different motion scales are also investigated from energetics point of view. The result shows that the maximum and minimum value areas of energy change on mesoscale fields are closely related to the intensity changes of mid and low latitude systems, and have rather good correlation with precipitation changes.