In practical applications, the thermoelectric module (TEM) conducts continuous heat exchange with the external environment. This causes uneven temperature distribution inside the module and some PN legs do not work effectively. The internal heat transfer direction of the TEM changes under the influence of the environment, resulting in energy loss and an inability to transfer heat in a consistent direction. In this study, the actual working environment of the TEM was simulated by a constant temperature heating platform, and we analyzed the heat transfer characteristics of the module using numerical calculation methods. Then, according to the results of this analysis, a sealed thermoelectric module (STEM) filled with high-temperature vulcanized silicone rubber (HTV) was designed. Besides, to improve the practicality of the STEM, we designed an integrated thermoelectric (TE) plate. The TE plate was equipped with a controllable water-cooling device, which allowed adjustments of the TEM cold end temperature according to the heat source to ensure maximum output power. Results indicated that the STEM can reduce heat exchange behavior at the edges and ensure uniform temperature distribution throughout the module. The maximum temperature gradient at the cold end of the STEM is 4.39 °C, which is 5.27 °C lower than the equivalent value of the TEM. Therefore, the temperature gradient in each of the PN legs in the STEM is similar, which can reduce the electrical loss generated by itself. We implemented a closed structure on the TE plate, and the internal circuit was installed on the contact surface of the water-cooling device to ensure that the circuit was not damaged due to the influence of the thermal environment. When the heat source temperature was 200 °C, the TE plate adopted a two-stage water-cooling mode to deliver a maximum output power of 78.64 W, which equates to a power generation per unit area of 0.86 kW·h/m². The TEM structure optimization and TE plate design scheme proposed in this study provides an efficient solution for the practical application of TE technology.