To improve the heat rejection efficiency of low Earth orbit (LEO) communication satellite and reduce the platform mass, through the analysis of the orbital heating flux of each honeycomb panel of in-orbit satellite, this paper proposes an inverted trapezoidal extension panel with heat pipes as conduction network. First, according to the integral average values of orbital heating flux of LEO communication satellite in orbit, the average heat rejection capacity of each honeycomb panel was obtained through numerical calculation, and the heat rejection performance of two box-type configuration schemes was compared. Then, in order to ensure the uniform temperature of honeycomb panels, a heat pipe network consisting of embedded heat pipes and external heat pipes was designed, so as to enhance the thermal coupling characteristics within and between honeycomb panels. Finally, the inverted trapezoidal extension panel configuration scheme was adopted for a LEO communication satellite, and hot and cold thermal balance tests were carried out. Research results showed that with the same area constraint, by using the inverted trapezoidal extension panel configuration, the heat rejection capacity of +X honeycomb panel was improved by 36.3%, -X honeycomb panel by 36.4%, +Z honeycomb panel by 10.2%, -Z honeycomb panel by 98.6%, and the heat rejection capacity of the whole satellite was improved by 34.6%, compared with the positive trapezoidal configuration. The thermal balance test results showed that the satellite platform met all temperature requirements under hot and cold cases. The whole satellite met the heat rejection requirement of 2 200 W, and the peak heat rejection was 870 W for the +Z panel phased array, indicating the feasibility of the inverted trapezoidal extension panel configuration based on the heat pipe network.