The invention discloses a boron concentration meter for a nuclear power station and a calibration method thereof. A detection device of the boron concentration meter is characterized in that a section of pipe on a drainage water monitoring branch is taken as a sampling pipe which serves as a sharing pipe section of a to-be-measured water monitoring branch and a calibration loop, and on-line communication of the sampling pipe and the calibration loop is realized through switching of tee branch control valves at two ends of the sharing pipe section; chemical titration as a standard, and the calibration for the boron concentration meter is finished ; and the operation is transferred to the monitoring branch after the calibration for real-time monitoring of boron concentration of primary loopwater . A measuring device adopts a linear mathematic model to establish a measurement relation in a piecewise fitting manner, so that the measurement precision is improved; and by means of an established on-line immediate calibration method, measurement drifting is eliminated, and measurement errors are corrected. The device is simple in structure, the measurement method is accurate and reliable, and the operation is easy; and by virtue of the calibration method, the insurmountable technical problem caused by enlargement of measurement errors of the boron concentration meter as time goes by is successfully solved, and accurate continuous on-line monitoring of the boron concentration of the primary loopwater is realized.