In order to solve the tracing problem of pollutant source in the subject of water environment, a backtracking model was built in this study to discern the source location and the emission time, based on the convection-diffusion equation and the genetic algorithm. By further introducing the decoupling method, the mass quality was also obtained. A concept of ‘weigh coefficient’ was introduced to improve the traditional genetic algorithm for high computational efficiency by controlling the evolutionary trend of population and optimizing the quality of population. Compared with the traditional genetic algorithm, the improved one makes the backtracking model more efficient and stable.