The total heat load on a train includes the loads by the train body,windows,fresh air,the human body and the equipment heat transfer,and its variation,which is related to the train operating environment and the passengers number,was calculated.The application of frequency conversion compressor was proposed to make sure that the actual unit load and the cooling load was in consistency as far as possible.With the help of MATLAB,the compressor speed and the frequency change rate in the actual circulation flow were determined according to the analysis on the ambient temperature,solar radiation intensity,train speed and passengers number.Compared with the solar radiation intensity,the change of the number of passengers has a greater influence on the compressor speed.