The invention discloses a plastic-steel door and window frame heat conduction modeling and calculating method. Based on a two-dimensional steady-state internal-heat-source-free heat conduction differential equation, a finite difference method is adopted to construct a frame and a temperature function of a closed cavity in the frame; boundary processing is carried out on the junction of the cavityand the frame by adopting a harmonic average method, and a heat conduction function at the boundary is constructed by combining with a difference method. The simulation calculation is carried out on the constructed mathematical model by using MATLAB under a third-class boundary condition to obtain a frame equivalent heat transfer coefficient. By using the method, mathematical characteristic analysis can be effectively performed on frame heat transfer. The boundaries of different materials can be well processed. The workload of simulation calculation is greatly reduced on the basis of ensuringthe model precision. The implementation of high-precision simulation calculation is facilitated.