This paper proposes an approach to evaluate the economics of pumped-storage units from the perspective of a multi-type power system. An MIP-based unit commitment model with various types of power sources is established, which integrates thermal, CCGT, hydro, wind, nuclear with pumped-storage units. Based on the model, the net present value of pumped-storage per megawatt is calculated. By comparing the net present value with the capital cost per megawatt, the economic evaluation of pumped-storage unit is conducted. The case study proves the feasibility of the model and the above approach. Furthermore, this paper analyzes the influence on the economic results of pumped-storage units by the change of peak-valley difference of the system load, the regulating range of thermal units, the capacity of nuclear and wind power, and the thermal-hydro proportion. The case study shows that the economics of pumped-storage is most influenced by the change of the capacity of nuclear and wind power and the thermal-hydro proportion.