Tropospheric delay errors, as the main error source of the continuous operating reference station system(short for CORS), must be corrected in high-precision positioning. In this article, several high precision fitting models are introduced, and their accuracy in different conditions is compared and analyzed. Combined with the advantages and disadvantages of the various fitting models, an improved fitting model is established. The new model, which is tested using measured data of Beibuwan CORS system (short for BBW-CORS) , proved to have good accuracy and stability.