Metal halide perovskite-based thermoelectric materials have garnered considerable attention due to their ultralow thermal conductivities and decent electric transport properties, while the research into thermoelectric generators (TEGs) lag much behind the progress of materials. In this paper, a real-sized 3D finite element model of a metal halide perovskite-based TEG is established under iso-thermal and iso-heat flux boundary conditions. Compared with traditional PbTe-based TEGs, perovskite-based TEGs exhibit more promising TE performance with TE conversion efficiency reaching ∼12 % at a 104 W/m2 thermal input power. In addition, the geometric parameters as well as the thermal management parameters under the iso-heat flux boundary condition, are optimized and discussed. The Taguchi optimization combined with the analysis of variance (ANOVA) method is further employed to quantify the contribution and importance of these factors on the output performance of the perovskite-based TEG. The results demonstrate that changing the device geometry and thermal management parameters will affect the temperature distribution between the hot- and cold-side. The thermal input power and the height of the p-n legs are the dominant factors affecting the output power and the TE conversion efficiency of the perovskite-based TEG. Promisingly, the TE conversion efficiency can reach above 20 % (or 65 % of the corresponding ideal Carnot efficiency) for an optimized perovskite-based TEG. This work predicts and verifies the highly promising TE performance of new metal halide perovskite-based TEGs. The principles behind the analyses here provide new strategies for designing and optimizing TEGs for waste-heat harvesting and other sustainable energy conversion applications.