Abstract: With the application of the hybrid algorithm of simplex method (SM) and the simulated annealing (SA) (SMSA),the function optimization problem is effectively solved in analyzing the data of water mass tracer test of river stream on the condition of instant injection of tracer to estimate such parameters as the longitudinal dispersion coefficient,the average stream velocity and the other parameter.With such different key parameters of algorithm as the number of inner loop,the cooling rate and the range of random disturbance in the new state generator,the simulation experiments are conducted to explore the effect of these key parameters on the convergence of the hybrid algorithm.The results show that the SMSA hybrid algorithm may be effectively applied to solve the function optimization problem of estimating water quality parameters of river stream,the conver-gence of hybrid algorithm is much better than that of improved simulated annealing with memory function in inner loop,the number of inner loop and the cooling rate have little effect on the convergence of hybrid algorithm,but much on that of improved SA,and the range of random disturbance in the new state generator may have clear evident effect on the convergence as on that of improved SA as well.