A disclosed determination apparatus for gas solubility comprises a gas chamber, a balance chamber, four valves, a vacuum pump, a stirrer, a magnetic stirring device, a temperature transmitter and a pressure transmitter; one side of the gas chamber is connected with the balance chamber via a pipe provided with a first valve; the bottom of the inner wall of the balance chamber is provided with the stirrer which is driven to rotate by the magnetic stirring device disposed at the bottom of the balancing chamber; the other side of the balancing chamber is connected with the vacuum pump and a high-pressure gas cylinder via a pipeline provided with the second valve; the top of the balancing chamber is connected with a balancing chamber cover in a sealed buckling manner; the balancing chamber cover is provided with the temperature transmitter and the pressure transmitter which are both connected with an analog quantity input module; and the analog quantity input module is connected with a computer. The usage method of the determination apparatus comprises preparation and determination of gas density in a liquid. The advantages comprise that the apparatus is simple and the operation is convenient.