With the widespread application of energy storage power stations in the power grid, due to the energy relocation of energy storage power stations, the impact of large-scale energy storage power stations on the power purchase characteristics of the power grid is becoming increasingly important. The production simulation program based on mathematical optimization is adopted to study the demand for electricity purchase and the power grid operation condition considering the start and stop of the unit, hydropower cross-week adjustment, pumping and storage cross-day adjustment, solar thermal power station cross-day adjustment. The influence of the power purchase curve mode on the amount of purchased electricity is studied, and the external power purchase mode is determined. Then the impact of the energy storage power station on external power purchase mode is analyzed. The simulation results of an actual power grid in northwest China show that compared with the straight-line power purchase mode, the step power purchase mode can reduce the amount of purchased electricity and new energy abandonment rate, but the maximum power purchase is increased. On the basis of the step power purchase mode, the construction of an energy storage power station can further reduce the amount of external purchased electricity, new energy abandonment rate and the maximum purchased power. It is recommended to adopt step power purchase mode and a 1 200 MW energy storage power station. The research results can provide references for the construction of grid-side energy storage station in high proportion of new energy systems in China.