The existing national standard photometric method can not directly determine the pollutants in the production process of continuous reaction units in the process industry. The main reason is that the absorption of ultraviolet light by oxygen in the deep ultraviolet region interferes with the detection of target substances by ultraviolet spectrophotometer, resulting in a certain degree of deviation in the detection results. Therefore, the key to solving this problem is to stably obtain the highly sensitive photometric information of substances with different characteristic wavelengths in the deep ultraviolet region. In this study, a nitrogen transmission and distribution system was installed based on a UV spectrophotometer. At the same time, an automatic injection flow cell and tray are designed to realize automatic sample injection between detection gaps. The nitrogen flows into the optical system area, sample room and data receiving area of the instrument is accurately controlled at 6, 2 and 3 L·min-1 respectively, so that the average value of the baseline flatness of the instrument is reduced from 0.108 to 0.010, which is 90.7% less than the air conditioner. Comparing the differences in the absorbance, sensitivity, sensitivity change and linear range of SO2-4 between air and nitrogen atmospheres, reveals that the absorbance and sensitivity of detection results in nitrogen atmosphere are improved in the range optical pathlengths b=1~100 mm. The sensitivity change increases from 10.42% to 30.65% when b=1 mm to b=100 mm, but the linear range decreases from 0.09 to 0.03 g·L-1 with increasing of optical path lengths. It shows that the nitrogen transmission and distribution system successfully inhibits the attenuation of UV intensity in the detection process. Compared with ion chromatography, one of the common methods for detecting SO2-4, this method has the advantages of convenient detection, stable and reliable detection results and good economic benefits, laying a foundation for industrial application.