Abstract: Bubbles are widely present in fields such as flotation, metallurgy, and marine engineering, and the evolution behavior of liquid films plays a crucial role in the coalescence process of double bubbles. Due to limitations in physical experimental conditions and in numerical simulation techniques, few studies have been able to directly observe the dynamic evolution of liquid films during bubble collisions. Based on the Basilisk software, this study employs the Direct Numerical Simulation method to investigate the evolution process of liquid film drainage during the collision of two bubbles in still water. By adopting an improved adaptive grid refinement method (with a minimum grid size of 10⁻⁷ m), the problem of liquid film rupture caused by insufficient resolution is effectively overcome, successfully capturing the microscopic dynamic evolution of the liquid film during the collision process. Based on the Direct Numerical Simulation results, a scientific criterion for determining the formation of liquid films is established. The results indicate that the initial liquid film thickness ranges from 10⁻⁶ m to 10⁻⁴ m, and increases with the increase of bubble size and collision velocity; that the evolution of liquid film length exhibits a two-stage characteristic over time—the first stage shows a relatively slow nonlinear growth, while the second stage transitions to a rapid approximate linear growth; and that bubble size has a small impact on the evolution of liquid film length. By combining theoretical analysis and DNS data, mathematical expressions for initial liquid film thickness and for liquid film length are established.