The invention discloses a calculation method of the power grid peak regulation margin based on peak regulation cost. The peak regulation cost of each time interval needed in the power balance is calculated by using the peak regulation cost of different gears during peak regulation and the peaking capacity value of the gears in the power balance. The functional relationship of the peak regulation cost and the peak regulation margin and the total peak regulation cost demanded in final power balance are used as indexes to present the peak regulation situation in the day. The method utilizes the calling condition of each gear peaking capacity and the calling cost so as to help plan decision-makers to evaluate the peak regulation situation and provide an important basis for the power system planning, design and power supply structure adjustment of a power system.