The working temperature of the crystalline silicon photovoltaic (PV) module seriously restricts the cell efficiency and the module lifetime. Therefore, it is of great significance to investigate the cooling effects of PV modules. Recently, introducing nanostructures into polymer backsheets to obtain direct-cooling effects due to enhanced heat conduction and radiation characteristics, has become a new trend for PV cooling technology. In this paper, we study the backside thermal properties of the PV module by combining the energy balance equation and optical simulations. The thermal power and cooling effect are calculated and compared between the standard backsheet and three types of direct-cooling backsheets for three typical ambient temperatures. The structure parameters and encapsulating mode of mainstream commercial silicon cells are adopted in the simulations and calculations. The influences of thermal parameters, i.e, the heat transfer coefficient and the emissivity, on the thermal process and the operating temperature are discussed in detail. We hope that this study may provide a certain reference for the future design of PV-direct-cooling backsheets.