High-power diode lasers are widely used in solid-state and fiber laser pumping. The spectral power distribution (SPD) of diode lasers should be perfectly matched with the absorption peak of gain materials. Spectral broadening would lead to a low optical-optical efficiency for the pump lasers. In this paper, a mathematical model based on multiple Gaussian functions was introduced to characterize the SPD of high-power diode lasers. The effect of temperature and the distribution on laser spectrum was specially included in this model. Temperature distribution in high-power diode lasers was calculated via an analytical three-dimensional thermal model. The temperature difference within the active region for diode lasers with different package structures and under different heat dissipation conditions was demonstrated. The intrinsic SPD for diode lasers with uniform junction temperature distribution was obtained from the experimental measurements in which a cold pulse current was injected into the diode lasers. SPDs for diode lasers under different injected currents were illustrated by this spectrum model, and compared to the experimental results for model validation. SPDs for the diode lasers with different chip architectures and packaging structures was calculated by coupling the analytical temperature fields into the spectrum model. Laser spectrum was verified to be independent of current density, but mainly depend on the junction temperature distribution in the experiments by comparing the spectra of the epi-up and epi-down packaged F-Mount single-emitters at same injected current. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.