Research conclusions ： The results come from analysis of the establishment of communication model and fitting of measurement of the actual road data ： With the frequency increases，the distance increases，building density increases， the transmission losses will increase. From the computer fitting results, the number of fitting parameters is more, the effect is better，but the computer fitting time is longer. So in the design of wireless communications, it is better to get a good result on selecting the appropriate transmission model and choosing the appropriate numbers of fitting parameters. It also provides a basis for modeling and design of GSM-R.