To investigate in numerical study the effect of largescale atmospheric environment on a tropic cyclone's track, a primitiveequation 10 level model was used, with an experimental scheme proposed for large-scale circulation experiencing remarkable adjustment. Results show that such adjustment goes through quantitative to qualitative change, suggesting that it experiences gradual (～24 h) to abrupt change, and a tropical cyclone, when right in the process of such adjustment, shows its precursor of abrupt change in its path that is given more clearly in the upper than in the mid-lower troposphere.