The pollard kangaroo method is a very effective way to solve the discrete logarithm problem in an interval of size N, which needs approximately 2 √N group operations under heuristic average case. For those fast inversion groups, Galbraith and Ruprai use equivalence classes method to lower the times of group operations which are needed under heuristic average case to approximately 1.36 √N.Based on Galbraith and Ruprai, this paper optimizes the method and adjusts the active interval of the tame kangaroos and wild kangaroos, in a way of changing each of their intervals to approximately 0.8581 times the original one, so that the group operations under heuristic average case is lowered to approximately 1.338√N.