Flow boiling within microchannels has been recognized as one of the most promising technologies for cooling high power equipment on modern aircraft. Due to experimental limitations, the mechanism of flow boiling under high flight acceleration is still unclear. The volume of fluid (VOF) method is used to numerically simulate the growth and departure of an isolated vapor bubble in a two-dimensional microchannel under high flight acceleration. A reliable and simple phase change model is employed to improve the accuracy of the flow boiling process. The numerical results show that the bubble growth process can be divided into three stages, including the free growth stage, the confined growth stage, and the elongated stage. The bubble growth rate increases sharply after the confined growth stage because the effective evaporation area between the bubble and the heating surface increases. Due to the confining effect of microchannels on the bubble, the magnitude and direction of acceleration have little effect on the bubble growth process. In addition, the effect of the feature size of the microchannel is investigated. In contrast to the results in the terrestrial condition, the bubble dynamics change significantly at high accelerations when the feature size of the microchannel is increased to 0.9 mm.