Abstract: Aiming at the phenomenon of over-range triggered quality bit anomaly of all three loop flowmeters during single pump operation in the commissioning of Hainan 1&2 units, the measurement method of loop flow rate and the measured data of flow signal in cold shutdown state are analyzed and studied based on the measurement principle of reactor coolant flow signal, shutdown protection logic and quality bit setting principle. This paper points out that the physical range of flow signal currently designed cannot envelope the relative flow rate value under various conditions. According to the analysis, it is necessary to adjust the measurement range of the flow meter so that the corresponding process flow range after converting the output 4~20 mA current is adjusted from 0~120%FP (FP is full power) to 0~129%FP (the loop flow signal shows X%FP, indicating that the current flow is X% of the relative flow rate during full power operation), and the current output of the flowmeters during the normal full power operation should be calibrated to 13.615 mA.