Physical and numerical model for a thermal radiation-electricity module in a TPV (Thermophotovoltatic) system is constructed. Current/voltage characters of the system consisting of a SiC emitter and GaSb or Si PV cells are obtained. Influences of emitter and cell temperatures are analyzed for a SiC emitter with GaSb cells. As emitter temperature rises from 1 400 K to 1 900 K, system electric power density increases from 0.67 W· cm^-2 to 5.43 W· cm^-2, and cell efficiency increases from 16.3% to 24.8%. However, the rise of cell temperature causes an opposite trend. As cell temperature rises 10K, system electric power density deceases about 0.15 W· cm^-2, and the cell efficiency deceases dramatically. The radiative energy distribution of a selective emitter with GaSb cells is discussed. Unusable radiative energy of the selective emitter can be reduced remarkably compared to a SiC emitter and thus improves system performance and stability effciently.