This paper presents a 2-dimensional finite volume model to investigate the performance of thermoelectric module (TEM) with polydimethylsiloxane (PDMS) encapsulation. The voltage and temperature distributions of the TEM under 2 kinds of boundary conditions (constant cold-side temperature and fixed convection heat transfer coefficient) are studied. To validate the developed model, 2 TEMs with or without PDMS encapsulation are fabricated, and the experimental tests are carried out. Both model predicted and experimentally measured results showed that using flexible PDMS as the encapsulation material for the TEM can lead majority heat flowing through thermoelectric legs and is beneficial for heat harvesting. The geometrical parameters' effects of the PDMS encapsulation and thermoelectric legs are analyzed. Results demonstrated that the usage of larger thermoelectric legs and smaller width of the PDMS encapsulation can generate greater temperature difference and hence improve the voltage of the TEM. Thus, the developed model could be applied for optimal structural design of the flexible TEM with highest performance for heat harvesting.