Abstract: Aiming at the optimal operation of the cascade hydropower plants with the characteristics of highly nonlinear and complicated constrain conditions,this paper presents the nested searching algorithm with the fractal division interpolation and chaos optimization.This algorithm uses the nested structure to unite determinate and stochastic searches,and can find out the global optimum according to its own regularity.The results of a practical example prove the nested algorithm's validity and practicability,and show it not only has many advantages such as strong ergodicity,simplified parameter configuration,high stability,global optimization,and easy programming,but also can get consistent convergence accurately and use less computing time compared with POA algorithm.Furthermore,the results also suggest the nested searching algorithm can solve the nonlinear optimal problems in the complicated constraint conditions and lay a foundation in the future study.