The invention discloses a mixing chamber technology-based gas metabolism detection apparatus and a method thereof. The apparatus comprises a gas collecting and mixing portion, a gas concentration analyzing portion, a control unit and a man-machine interaction device, the gas collecting and mixing portion comprise a breathing face shield, a T-shaped valve, a flow sensor, a mixing chamber 1 and a mixing chamber 2, and the gas concentration analyzing portion comprises a low concentration calibrating gas bottle, a high concentration calibrating gas bottle, a four-way solenoid valve, an oxygen sensor, a carbon dioxide sensor and a suction pump 2. The pre-positive mixing chamber 1 greatly accelerates the mixing speed of expired gas, eliminates the large fluctuation of the concentrations of oxygen and carbon dioxide in the expired gas, shortens the gas mixing time and improves the analysis real-time property; and the post-positive mixing chamber 2 effectively intercepts and mixes five expired gases by means of a baffle plate, and allows the average concentrations of oxygen and carbon dioxide in the gas in the mixing chamber 2 to be accurately obtained.