The invention discloses an adjustable peak energy storage system based on supercritical carbon dioxide circulation and a control method thereof. The system comprises a low-pressure supercritical carbon dioxide storage tank, a first compressor, a first heat exchanger, a first cooler, a high-pressure supercritical carbon dioxide storage tank, a low-temperature brine storage tank and a high-temperature brine storage tank; a first outlet of the low-pressure supercritical carbon dioxide storage tank is connected with an inlet of the first compressor through a first control valve, an exhaust port ofthe first compressor is connected with a first inlet of a first heat exchanger, and a first outlet of the first heat exchanger is connected with an inlet of the high-pressure supercritical carbon dioxide storage tank through the first cooler and a second control valve; and a second outlet of the first heat exchanger is connected with an inlet of the high-temperature brine storage tank, and an outlet of the low-temperature brine storage tank is connected with a second inlet of the first heat exchanger through a fourth control valve. By the adoption of the system, peak shifting and valley filling can be effectively realized, the power cost of a user can be well reduced, and the capability of the user to accept an intermittent energy source can be improved.