The concentration of SO₂ gas in the atmosphere is very low, and therefore, the emitted fluorescent signal is weak, directly impacting the detection accuracy of SO₂ gas concentration. Owing to these issues, the optical path for traditional fluorescence collection is long, hindering the development of the miniaturization of instrument. To improve the collection efficiency of fluorescence signals and the detection accuracy of the instrument by shortening the traditional optical path, we used the ZEMAX software to design an optimized trace SO₂ fluorescence signal collection optical path for a random divergent distribution of fluorescence. We then compared the results from this path with those from the traditional fluorescence collection optical path. Simulation results show that the collection efficiency of optimized fluorescence collection optical path is approximately 22.6%, which is 4 times that of the traditional fluorescence collection optical path. The distance from the image-based main point of the lens group to the optimal collection point is reduced by 29.17%. The optimized optical path in this paper is beneficial for further improvements in the miniaturization and detection accuracy of the existing atmospheric trace sulfur detection instrument.