Abstract: The boric acid concentration measured from boron meter and chemical analysis deviates from each other in the process of reactor unit operation. In this paper, we use the experimental data from QSⅡ nuclear power plant to analyze the influence of 10B abundance on the deviation. We find out that the deviation will reach a maximum value during the MOL, and some advice on the operation of the plant is proposed according to this phenomenon. Whats more, we calculate the boric acid concentration through ORIENT and verify its reliability by comparison with chemical analysis. As a consequence, we can predict and monitor the changes of boric acid concentration in the core of reactor more accurately.