To enable the stable operation of diode-pumped lasers without temperature control in a wide temperature range, the influence of the emission spectra of laser pump sources on the stability of laser systems is analyzed. Taking into account the energy utilization efficiency of the pumping process, an optimization scheme for the pump source spectra of lasers without temperature control is proposed. The scheme can effectively reduce the influence of the wavelength drift of pump sources on the absorption efficiency and thermal focal length of laser systems, thus making lasers work stably in a wide temperature range without temperature control. In the operating temperature range from -40 ℃ to 60 ℃, the optimal emission spectrum of a pump source is calculated for a Nd∶YAG laser system with different absorption lengths and doping concentrations (atomic number fractions). In theory, compared with a conventional single-wavelength laser diode (LD) pump sourse without temperature control, the pump source designed by this scheme can significantly improve the working stability of laser systems and reduce the fluctuations of absorption efficiency and thermal focal length to less than 13% and 16% respectively. A LD pump source with two wavelengths (803.7 nm@10 ℃ and 809.2 nm@10 ℃ with proportions of 68.4% and 31.6% respectively) is designed for the Nd∶YAG laser system with an absorption length of 30 mm and a doping concentration of 0.8%. The simulation results show that within the temperature range from -40 ℃ to 60 ℃, the absorption efficiency of pump light remains above 90.7%, and the absorption stability and thermal focal length stability are 91.4% and 85.4%, respectively.