The invention discloses a pressurizing solution dehumidifying air conditioner based on expansion work. The pressurizing solution dehumidifying air conditioner comprises a steam compressing refrigerating circulating loop, a solution circulating loop and an air processing loop. The steam compressing refrigerating circulating loop comprises a compressor, a condenser, a first expansion compressor and a high-temperature evaporator. The solution circulating loop comprises a condenser, a second expansion compressor, a dehumidifier, a solution throttle valve, a dilute liquid storage tank, a dilute solution pump, a liquid-liquid heat exchanger, a regenerator, a concentrated liquid storage tank, a solution cooler and a solution pressurizing pump. The air processing loop comprises a first expansion compressor, a dehumidifier, a second expansion compressor, a high-temperature evaporator, a regenerator and a fan. By the air conditioner, low-concentration dehumidification is achieved, and condensing waste heat is used for solution regeneration and heat-humidity independent processing. The invention further discloses a control method of the air conditioner, the method includes steam compressing refrigerating circulating, solution circulating and air processing circulating which are performed simultaneously, and the method is simple to operate.