A server, a communication system, and a positioning method based on mobile network thereof are provided. In the method, a first measurement report and a second measurement report are received. The first measurement report is related to a first network performance measurement of a user equipment (UE) with a mobile network and includes first location information of the UE, and the second measurement report is related to a second network performance measurement of the UE with the mobile network. The Second location information of the UE is determined according to a monitoring result obtained from the second measurement report. The monitoring result is related to the signal transmission condition of the UE in the mobile network. The second location information is calibrated according to the first location information. Accordingly, the accuracy of the location of the UE may be improved.