Cold cesium atoms are obtained using magneto-optical trap (MOT) technology. Under different trapping laser powers, the collisional loss rate coefficients for cold cesium atoms were measured by observing the fluorescence intensity variance of cold atoms clouds when MOT was loading. The experiment was achieved in a single trap, thus it is convenient and easy. In addition, it is found that the collisional loss rate coefficient depends on and increases with trapping laser power, which is in agree with the Gallagher-Pritchard theoretical model. It validates that the radiative escape and fine-structure-changing collisions are the main reasons for cold atoms lossing in a MOT. The results are of significance for further improvement on trapping efficiency of MOT.