A simulation procedure for the transient process of closure of guide vanes of a turbine is programmed by MATLAB software, and then the influences of three key factors, i.e., the first closure time, the second closure time and reflecting point opening of guide vanes, on the rotational speed of the unit and the dynamic pressures in the spiral case are discussed. The values of the three key factors may be determined from the curves obtained calculated results of an illustration respectively, namely, the first closure time being 6 seconds, the second closure time 12 seconds and the reflecting point opening of guide vanes 65%. Finally, the closure laws of guide vanes are optimized by obtain ed parameters, and the contradiction between the arising of rotational speed of the unit and the enhancing of dynamic pressures in the spiral case is harmonized effectively. 