The invention discloses a calibrating method of a steam turbine monitoring system. The calibrating method comprises the following steps that (1) mounting of sensors is conducted, specifically, the bearing vibration sensor, the shaft vibration sensor, the axial displacement sensor (10) and the rotating speed sensor are mounted; (2) calibrating is carried out, specifically, a vibration display numerical value is obtained by measuring a bearing vibration measuring point, a vibration display numerical value is obtained by measuring a shaft vibration measuring point, a displacement display numerical value is obtained by measuring an axial displacement measuring point, and a rotating speed display numerical value is obtained by measuring a rotating speed measuring point; and (3) calibrating result and qualification judging is conducted, specifically, according to recorded standard instrument indicating values and the actually measured values, the bearing vibration measuring point, the shaftvibration measuring point, the axial displacement measuring point and the rotating speed measuring point have relative or absolute errors, bearing vibration, shaft vibration and axial displacement have the relative errors, and the rotating speed has the absolute error, when the calibrating results of all the measuring points are within the maximum allowance error, it is shown that the steam turbine monitoring system operates normally, and when the calibrating result of a certain measuring point exceeds the allowance error, it is shown that the error at the measuring point is generated at a TSIcabinet or at a DCS link, and further troubleshooting continues.