The main idea of the optimal model for power system peaking units' expansion planning considering weekly regulation pumped storage power station's operation characteristic is studying out all capable peaking units' combination schemes which satisfy the load development and the constraint condition in each year of planning period. Then the technology and economic factors of each peaking units' combination scheme are figured out and analyzed, and finally the most economic peaking units' combination scheme considering the whole system and the planning period is obtained. The proposed model is used for the optimization calculation of the HP pumped storage power station in a province. The results show that power station with weekly regulation and station with daily regulation have the same ability in substituting thermal station. Weekly regulated station has more benefit in economy and saving coal, but not so good as daily regulation in peaking. (5 pages)