Laserprojection displacement meter (LDM) is widely utilized for bridge deflection monitoring. A comparative calibration method is proposed to fulfill the online and insitu calibration requirement of LDM. First, a laser displacement meter with traceable calibration is adopted as the reference sensor (RS). The insitu measured value series by the RS and the LDM under calibration are acquired simultaneously under the same timevarying excitation source. Then, two series are matched based on feature points sectioning method. The phase differences caused by the variation of excitation source and diverse response characteristics of sensors are solved. The sequentially comparative measured values with the certain inputs are obtained. Finally, the statistical analysis is performed to the matched data series, which can produce the result of LDM under calibration. An online calibration simulation system is designed and set up according to the real insitu condition. A verification subsystem using laser interferometer as a reference is adopted to evaluate the proposed method. Experimental results show that the proposed method has a high consistency with the method of simultaneously comparative measurement by using laser interferometer as a reference. Especially, the proposed method can be used under insitu conditions of bridge deflection monitoring application.