Abstract: Aimed at the sensitive area issue in tropical cyclone (TC) observation, the GRAPES-CM is used to make sensitivity experiments for the TC Prapiroon and the TC Sepat which made landfall at China. The results are compared with the simulative results for the tracks of four other tropical cyclones. The comparative results show that the uncertainty in the initial fields leads to the track uncertainty, but the initial vortex uncertainty has nearly no impact on the track. The cirque in the environmental field is the sensitive area which impacts the TC track. The cirque’s inner boundary borders the vortex. The distance between the cirque’s outer boundary and the TC center is about 500 km. The uncertainty magnitude in the cirque initial fields determines the track uncertainty magnitude. In the cirque, the perturbations in the different area grow differently during the simulation, resulting in that the changes in the different area are able to impact the track differently. This difference is related to the TC environmental pattern. At the different height the impacts on the TC track differently as well. The changes in the high or low layers have little impact on the track while the impact of the changes in the middle layers on the track is high. The middle layers’ mean wind is just the environmental steering flow which governs the TC motion. Basis can be obtained from these results for the TC observations made in China in the near future.