In practice, the output energy stability of a light source affects the reliability and performance of the light source in various applications, such as laser therapy, spectral analysis, photoelectric countermeasures, and optical imaging. In this paper, the output energy stability of the optical parametric oscillator (OPO) system is first analyzed from three aspects, laser pumping source, resonant cavity structure and nonlinear crystal. Experimentally, a pulsed laser-pumped 3~8 μm mid-infrared OPO radiation source is constructed using a BaGa₄Se₇ (BGSe) crystal, and the output energy fluctuation is measured and analyzed in detail from both the laser pumping source and the OPO system. When the input pump energy is 30 mJ and the positive-incidence output is 4.5 μm, the average energy is 2.151 mJ with a standard deviation of 56.49 μJ, and the calculated RMS fluctuation is 2.62%. According to the analysis, it is concluded that the fluctuation of the output pulse decreases with the increase of the laser gain and the decrease of the cavity loss. This study provides a useful guide for the selection of operating parameters of infrared radiation sources with BGSe crystals in different application scenarios.