The role played by environmental background and inner core in the changes of intensity o f Typhoon Neoguri is documented by using observed track data, NCEP Final Analysi s, NOAA OI SST weekly means and FY satellite water vapor images. The results sho w that (1) the storm weakening is closely related to the vertical wind shears a nd sea surface temperature. The vertical wind shears increase in magnitude to about 10m/s, and the Maximum Potential Intensity (MPI) decreases when the system moves over a cool tongue of water, the intensification comes to an end; (2) The breakdown and recovery of eyewall revealed by vapor images, are consistent with intensity changes. The breakdown (recovery) of eyewall leads to the storm weakening (deepening).