A parallel one-dimensional model for transient thermal analysis of the metallic thermal protection system (MTPS) for reusable launch vehicle (RLV) is established. Firstly, several heat roads are defined according the structure of the MTPS. The implicit differential formulation of single heat road is given after the discretization of heat roads. Then, the local control equations for series-wound and parallel public nodes are given with the heat equilibrium method. Furthermore, the uniform formulas of the usual boundary conditions are presented. Finally, the global control equation is gained. The transient temperature field is obtained with numerical calculation. The results show that the heat transfer process can be predicted more credibly and accurately by the adoption of the parallel one-dimensional model, which can also provide a more valuable reference for the optimization design of MTPS.