Abstract: High concentration heavy water is used as moderator and coolant in a reactor, and its concentration closely related to the safety and performance of the reactor. It is very important for the reactor safety as well as health of operating personnel to quantify the heavy water concentration accurately. The bubble is one of the main factors that affect the accuracy of determination for heavy water concentration via infrared spectrometry. Specifically, bubbles cause distortion in the infrared spectrum of heavy water, leading to quantitative deviation in heavy water concentration. A method for on-line identification of bubbles in high concentration heavy water based on single beam spectrum was proposed as the bubble effects the appearance of infrared spectrum. Firstly, absorption spectrum and the single beam spectrum were acquired respectively with or without bubble. Secondly, the characteristics of absorption spectrum and the single beam spectrum with bubbles were extracted respectively. Research shows that the method based on single beam spectrum has more advantages than the method based on absorption spectrum in on-line quantitative analysis of heavy water concentration. Thirdly, a program method for quantitative analysis of high concentration heavy water and bubble identification based TQ Analyst, Micro Basic and Omnic 8.0 is established. Fourth, the concentration of heavy water was quantified and the presence of bubbles in the cell was identified. The accuracy of bubble identification by absorption spectrum and single beam spectrum is 100% when the number of the samples is 500. Consequently, the technical challenge of detecting abnormal data caused by air bubbles during the on-line infrared spectrometric determination of high-concentration heavy water is successfully overcome.