In order to explore how to choose the turbulence model of the gas-liquid two phase flow in a horizontal pipe, the guess that the turbulence of the interface of the gas-liquid two phase flow in a horizontal pipe is anisotropic was put forward. The emergence and development mechanism of the turbulence anisotropy in the interface was analyzed. It points out that the turbulence inertial force generated by the turbulence anisotropy in the interface is an important reason for the formation of annular flow in a horizontal tube, which was verified by comparing the simulation results of using the two-equation model and Reynolds stress model (RSM) to simulate the same working condition of annular flow in a horizontal tube. On such basis, the basis of selecting turbulence model in gas-liquid two phase flow was discussed. The results show that the RSM model is adaptive for large gas-liquid shear stress in a horizontal pipe, while the two-equation model and RSM model are both adaptive for other conditions.