Tropical cyclone path forecast results are checked for 2012 to 2013 using the GRAPES_TYM model. The results show that the average distance errors of the model is 94.3, km, 143.7 km and 260.8 km, in 24 h， 48 h and, 72 h, respectively; there exist farthernorthern systematic biases for all types of TC forecast paths for the GRAPES_TYM model; for TC in the South China Sea, the TC moving direction prediction by GRAPES_TYM model slants to the right, and the moving speed error is less. The moving direction deviation is the main source of the path deviation. In addition, the statistic prediction model bias toward TC and TC environmental steering flow forecast bias are closely related. Taking the Typhoon “Kaitak” as an example, according to the moving direction error diagnosis equation, the environmental steering flow forecast deviations (including environment wind field deviation, the impacts of the environment directing flow radius deviation, and environmental steering flow thickness deviation) on the TC moving direction prediction error are investigated; however, the environmental steering flow forecasting error sources are related with the model forecasting errors of largescale weather systems and the size and strength of TCs.