The evolution of the rainfall level of the city of Kolwezi (DRC) from 1953 to 2010 allowed us to distinguish the period of low precipitation from that of heavy precipitation. The frequency polygon of the Kolwezi rainfall distribution is an asymmetric curve spread to the right and shows that a normal log-law would be suitable as a probability model. This law is that of GALTON. For the estimation of the parameters of the nonlinear model having no indication of the errors of the measurements, we used the method of least squares whose optimization was made using a software algorithm MATLAB.