Abstract: In December 2017, the gas radon meter was upgraded to BG2015 emanometer. In December 2018, the ATG6138M trace mercury meter was applied in gas observation. The two sets of instruments used the same degassing device. The record shows that the data dispersion of the original system of gas radon meter and gas mercury meter is large. The reason of data dispersion is that the well flow rate is reducing year by year, which makes the original degassing device shows its drawbacks. Because of the design defect, the small water intake of the collecting chamber results in the phenomenon that the original outlet cannot realize the water-sealed so that making air run off. On the other hand, the ATG6138M trace mercury meter has a function of induction air in certain time. There are some water-gas inhaled into instruments in the original device because of the small distance between the liquid level and the degassing port, which causes instability of the instrument. For this reason, we carry out targeted design to solve the defects of the original degassing device. The monitoring data shows that the defects of the original degassing device have been solved.