Abstract: The compared analyses between two tropical depressions in South China Sea arc c by using the numerical model developed in Guangdong Institute of Tropical and Oceanic M logy and ECMWF data,one of which developed into a typhoon in 24 hours,and the other loped. The analyses show that their initial humidity and temperature fields have ent vertical structures, with the developing one has a deep high-humidity layer and a clearcored structure in the mid-lower troposphere, and the undeveloping one has not a warm structure in the lower troposphere and the humidity in the midlower troposphere is smaller.ral numerical tests, by changing their vertical structure of humidity and ien.-perauire in sion area, show that the humidity and temperature structure in the depression area play roles in the development of depressions. It is favourable to development of depres deep high-humidity layer or a warm-cored structure exist in the mid-iower troposphe versely, it is not favourable to the development of depressions when the humidity there is no warm-cored structure in the mid-lower troposphere. And these effects of temperature structure on the development of depressions occur most pdepth or strenth of conditional instable layer and vapor suply condition in theWhich leading to the change of convective development. Finally, the sensitivity ment of depressions in the South China Sea to the change of humidity and pression area is discussed.