Abstract A plate-type thermoelectric generation (TEG) system is typically used in engine exhaust waste heat recovery systems because of its appropriate structure. To obtain an effective design of these TEG systems, this study focuses primarily on optimal matching performance analysis, by building a complete numerical TEG model with the finite element method using FORTRAN. A commercial-type thermoelectric material is used in the numerical calculation. Moreover, all types of work conditions with different exhaust parameters (mf = 10–50 g s−1 and Tfin = 300–600 °C) and cooler’s heat transfer processes are included. When peak net power is achieved, all corresponding optimal features are analyzed, where both air-cooling and water-cooling methods are considered. The results indicate that, for any type of work condition, the optimal height remains the same (Bopt = 7.0 mm for the air-cooling method and Bopt = 4.0 mm for the water-cooling method) and the other optimal parameters can be expressed by fitting correlations, which can deduce the optimal length (Lopt) and width (wopt) of an exhaust heat exchanger (for example, they are Lopt = 1.55 m and wopt = 0.78 m when mf = 50 g s−1, Tfin = 500 °C, and hc = 80 W m−2 K−1 for the air-cooling method). The introduced fitting correlations are verified to have a high accuracy.