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Gas bubble formation behavior in the wellbore has influence on wellbore temperature and pressure by varying bubble movement characteristics. For now, most researches on gas bubble migration along the wellbore bases on bubble bed gas-liquid two-phase flow models in chemical industry, which is far away from the reality of the situation of wellbore during drilling process. Bubble channel is perpendicular to gravity and buoyancy during drilling, but it is parallel to gravity and buoyancy in the chemical industry. Based on computational fluid mechanics, gas bubble formation which channel perpendicular to buoyancy and gravity is simulated using CFD, the process of gas inflow, gas bubble formation and departure is analyzed. The flow field changes around bubbles and influential factors of gas bubble formation are also studied in this paper. Simulations indicate that the shape of the bubble during gas kick has always maintained asymmetric over development process. Formation pore radius and fluid density have significant effect on departure radius and time of gas bubbles, while the influence of fluid viscosity is slight. The main contribution here is that gas bubbles formation characteristics in bottom hole are revealed based on bubbles accumulation rules of bottom hole. [ABSTRACT FROM AUTHOR]