In order to study the mass transfer between the free gas and oil in a fluid power system and realize bubble mass measurement in oil, the radius limit of the bubble during measurement was derived from steady state and zero temperature gradient conditions. A high-pressure gas-oil mass transfer optical measurement system was designed, and the key algorithms for bubble identification and tracking were studied. First, the radius limit of a bubble during measurement was derived from the Biot number and Newton's Law of Cooling, and a high-pressure gas-oil mass transfer optical measurement system was designed. Then, a method to identify bubble elements from a video was demonstrated, based on the roundness of a circle and a set threshold. Finally, a minimum vector length method was used to track the center of a bubble between frames. Experimental results indicate that the system can achieve optical measurements under a pressure of 14 MPa, and the error for measuring the radius of the bubble is within 4%. The experimental method for gas-oil mass transport study can satisfy the system requirements of optical measurement of gas-oil mass transfer in a fluid power system.