Abstract: The Continuously Stirred Tank Reactor (CSTR) Model is one of the most commonly used river water quality models in the world. The hydrological model plays a key role in the model's numerical stability, but this problem has not been fully discussed until now. With the river section from Chaoyang Water Plant to BayiBridge in Ganjiang River as an example, based on the field observations, the numerical stability, accuracy and efficiency of Runge-Kutta-Felberg (RKF), classical Runge-Kutta (RK4) and implicit Runge-Kutta (RK2) were compared by tank-by-tank integration and whole river integration respectively. It shows that although the tank-by-tank method is used much extensively, the stability of the whole integration is superior to the tank-by-tank integration. The stability of the three Runge-Kutta methods is in the order of RKF