A dynamic calibration system for calibrating a moisture sensor comprising a programmable logic device as a processing unit, and an analyzer comprising a moisture sensor configured to accept a subject sensor element, wherein an output of the moisture sensor is connected to the processing unit, the processing unit including: a functional logic circuit of said programmable logic device configured to obtain reference data from a calibrated reference sensor element installed as the moisture sensor, which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into the analyzer; a functional logic circuit of said programmable logic device configured to obtain subject data indicating temporal variation of output-responses of a subject sensor element to be calibrated installed as the moisture sensor of the analyzer (34, wherein the subject data are obtained under the same condition as the reference data; and a functional logic circuit of said programmable logic device configured to compare the subject data to the reference data with same time-duration measured from a timing at which the water-vapor with the known concentrations is injected for calculating relationships between the output-responses of the subject sensor element and the known concentrations, the system further comprising: an injector configured to inject a constant volume of a calibration gas to an inlet configured to receive a tip of the injector; a flowmeter configured to control a flow rate of a background gas; a first pipe for introducing the background gas to the flowmeter; a second pipe connecting the flowmeter with the inlet, configured to flow the background gas at a controlled flow rate by the flowmeter; and a third pipe connecting the inlet with the moisture sensor, configured to introduce the background gas and the calibration gas into the moisture sensor. a functional logic circuit of said programmable logic device configured to obtain reference data from a calibrated reference sensor element installed as the moisture sensor, which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into the analyzer; a functional logic circuit of said programmable logic device configured to obtain subject data indicating temporal variation of output-responses of a subject sensor element to be calibrated installed as the moisture sensor of the analyzer (34, wherein the subject data are obtained under the same condition as the reference data; and a functional logic circuit of said programmable logic device configured to compare the subject data to the reference data with same time-duration measured from a timing at which the water-vapor with the known concentrations is injected for calculating relationships between the output-responses of the subject sensor element and the known concentrations, an injector configured to inject a constant volume of a calibration gas to an inlet configured to receive a tip of the injector; a flowmeter configured to control a flow rate of a background gas; a first pipe for introducing the background gas to the flowmeter; a second pipe connecting the flowmeter with the inlet, configured to flow the background gas at a controlled flow rate by the flowmeter; and a third pipe connecting the inlet with the moisture sensor, configured to introduce the background gas and the calibration gas into the moisture sensor.