Abstract: A two-dimensional transient numerical model with interphase coupling is established in this study. The flow and heat transfer characteristics of cylindrical heat pipes with Trapezoidal Groove -mesh composite wick are studied under horizontal placement conditions. The porous media model and User-Defined Function (UDF) are employed to simulate the fluid and heat transfer processes within the heat pipe. The results show that, compared to a single-structure wick, the trapezoidal groove-mesh composite wick modifies the internal flow channels, which alters the flow characteristics of the working fluid. Specifically, with the widening of the wick channel, both the velocity and pressure drop of the liquid phase decrease. Meanwhile, the contraction of the vapor core channel increases the velocity and pressure drop of the vapor phase. The high-mesh wick contributes to reduce the overall thermal resistance of the heat pipe due to its high thermal conductivity. However, its low permeability increases flow losses and weakens the working fluid's return capability. Moreover, increasing the heat flux of the evaporation section enhances heat transfer efficiency, while simultaneously inducing significant vapor and liquid pressure gradients, thereby further constraining the reflux driving force.