The invention discloses a control method for improving the deep peak shaving capability of a power plant, which belongs to the field of operation and control of a power system. In a condition of insufficient peak shaving capability of a thermal power unit, a high-capacity electric heat storage device is arranged at a thermal power plant side, and thus, the deep peak shaving capability of the thermal power plant is improved. The power plant output is improved, the amplitude is reduced, the deep peak shaving capability of the power plant can be effectively enhanced, and the number of power plants with the deep peak shaving capability is increased. Through arranging the electric heat storage device, heat supply and power supply of a cogeneration unit are promoted to be effectively separated,the power supply flexibility of the cogeneration power plant is improved, and the heat supply capability is effectively improved.