The kinetics of gas phase dissolution and exsolution in air-liquid H₂O system was studied by in-situ observation of hydrothermal diamond anvil cell combined with high-speed video recording. The process of bubble growth and dissolution was recorded in situ. The reaction times and temperatures were determined accurately according to the photos decomposed from the video files. The volume growth parameters and dissolution degree of bubbles were calculated by the changes of bubble radii recorded with time. Cooling process of gas-liquid homogeneous system promoted bubble to dissolve, and the bigger cooling rate was, the faster bubble appeared. With temperature changes, the radius of bubbles which in the gas-liquid equilibrium system experienced three stages: the radii of bubbles decreased rapidly with time in the initial heating stage; the radii of bubbles varied slightly in the middle stage due to the expansion caused by the decrease of temperature and pressure; and then bubbles continued to dissolve until disappeared on the final stage which dissolution rate was smaller than that is in the initial stage. In the multi-bubbles system, the dissolution rates were not related to the radii of the bubbles at the initial heating stage, but negatively related to the radii of the bubbles at the final stage of dissolution to disappear: the smaller the radius, the larger the dissolution rate.