Abstract: The blow-type liquid level measuring instrument for the radioactive waste liquid treatment system in the nuclear power plant is frequently blocked, resulting in the loss of monitoring of the radioactive waste liquid level, thus affecting the efficiency of the radioactive waste liquid treatment. A new automatic purging device for preventive purging of the blown liquid level measuring instrument is added. According to the blown liquid level measuring instrument of measurement of gas path composition and clogging cycle, the purging gas path of the automatic purging device is recombined with the measuring gas path, and the purging logic ensures the purging work by setting the sequence and time interval of starting and stopping the purging work.  Only one measuring gas path is purged at a time, and the measuring function of the meter is not affected. The automatic purging device solves the problem of frequent blockage of the measuring pipeline of the blow-type liquid level meter, and finally ensures that the liquid level monitoring function of the radioactive waste liquid is available. The results show that the application of the automatic purging device is conducive to the continuous monitoring of the liquid level monitoring function of the blowing liquid level measuring instrument, without interference with the radioactive waste treatment.