In a CDMA system, energy from all users occupies the same bandwidth at the same time. Therefore, each user is considered as an interference source to the other users. Recently, there are a lot of papers and test reports discussing about the interference in a CDMA system for the purpose of estimating the system capacity more precisely. In this paper, the interference in the reverse link within the same cell is studied. According to the mathematical analysis and proper system model, the probability that describes the user controlled by one given cell is drawn. Base on the result, both the average value of the same-cell interference and the percentages of each interference component are obtained in the different propagation environments.