Abstract: Studying the bubble departure radius in the liquid oxygen tank under microgravity is the basis for the propellant boiling and heat transfer calculation of the launch vehicle propulsion system in orbit. Unlike regular or low gravity environments, the Marangoni effect becomes essential in microgravity. To calculate the bubble departure radius, Firstly, a bubble dynamics model is developed, including buoyancy, inertia, pressure, surface tension, drag, and Marangoni forces. Secondly, to solve the problem of the narrow application range of the existing Marangoni force formulas, a more accurate correction factor is fitted by numerical simulation. Consequently, the Marangoni force model is extended. Finally, using the physical parameters of saturated liquid oxygen at 0.3 MPa, a conventional working pressure for the liquid oxygen tank of the launch vehicle, the change of the total force with the radius and the departure radius with gravity are calculated, respectively. The results show that bubbles' departure behavior can be divided into three zones: microgravity zone, transition zone, and low gravity zone. The microgravity zone can form large bubbles of a centimeter or even meter scale, while the low gravity zone can only form tiny bubbles of 0.1 mm scale. Compared with the previous models, the model in this work can be applied to all three zones. Therefore, it comprehensively reveals the bubble departure characteristics in the liquid oxygen tank under microgravity. It can also provide theoretical support for analyzing the heat transfer characteristics in the liquid oxygen tank.