In order to increase the successful rate of the original complex optimization algorithm

the mutation particle swarm optimization (MPSO) calculation would be introduced for all design points of the initial complex and the current complex while the mapping of the bad design point was unsuccessful firstly. One of the design points is replaced by a point with quasi-optimum object function value that has been gotten by the MPSO based on the substitution rule of maximum complex central distance; and a new complex has been formed. The original complex optimization calculation would be continued with the new complex until the stopping criterion. The improved complex method is applied to searching minimum safety factors in two complex soil slopes; and the result has shown that the method is much more likely to locate the true minimum.