Abstract: COSINE is an integrated code package for nuclear power plant core and safety analysis independently developed in China, in which the sub-channel code cosSubc-2F adopts the modeling method of two fluids and three-phase fields（i.e., continuous liquid phase, droplet phase, and gas phase）. Except for the energy conservation equations shared by continuous liquid phase and droplet phase, each phase contains mass, momentum and energy conservation equations, totaling eight independent conservation equations. In sub-channel codes, the core fuel assembly is divided into several parallel sub-channels, and the sub-channels are not closed. The mass, momentum and energy exchange of fluid occurs among the sub-channels due to pressure gradient and other factors. As the key model for the interaction between channels, the turbulent mixing and the void drift model is very important in the sub-channel code. In this paper, the mechanism of turbulent mixing and the void drift model in the sub-channel code cosSubc-2F is introduced in details, and a series of experiments are selected for testing. The effectiveness of turbulent mixing and the void drift model in this code is fully verified. Through the comparative analysis of the results, some suggestions for the development and optimization of the model are put forward.