Abstract: The mathematic mode based on rate equations and power propagation equations of Tm3+-doped silica fiber lasers is established and calculated by Matlab software. Output mirror reflectivities of the laser power, optimization of the fiber length and dopant concentrations may significantly improve the slope efficiency of fiber lasers. The evolution of small signal gain coefficient without upconversion and with upconversion is showed for different pump powers. The distributions of the pump light and laser along the fiber and the ion concentrations at every energy level are analyzed. The relation between the small signal gain and incident pumping power, as well as the relation between the pumping light and laser powers with gain medium length are investigated at different dopant concentrations. The relation between output powers and different output coupling mirror reflectivities is studied at different pumping powers. And the further research is also carried out on the relation of slope efficiency and pumping threshold versus fiber lengths for different pump absorption coefficient. The results indicate that there are optimal fiber length and optimal coupling output transmissivity for the maximum of laser output power.