The instrument adopts ultraviolet absorption method. The basic working principle is: ozone can absorb ultraviolet light with wavelength of 254nm, and the intensity of ultraviolet absorption is related to its concentration. The method of sample gas detection is as follows: using low-pressure mercury lamp to emit ultraviolet light at 254nm, irradiating in the detection chamber, alternately passing the sample gas (containing ozone sample gas) and reference gas (sample gas after removing ozone), through the light intensity ratio of the two, the O 3 in the sample gas is calculated by Lambert Beer law One is used as the sample gas light path, the other is used as the reference light path to monitor the change of the zinc lamp light source to automatically compensate for the change of the light source.