Traditional electrical displacement sensors usually are big and insensitive, difficult to multiplex, therefore, they are not suitable for model test. In this paper, a novel subminiature multipoint FBG displacement sensor which has overcome the shortages of above displacement sensors is designed especially for the model test based on analysis of displacement detecting principle. It mainly consists of several FBGs, springs, crusts and the bases. FBGs which are sensitive device connect with springs in series. When key point moves, stretching deformation of spring will occur, so that FBG will receive axial force which will make central wavelength of FBG drifts. According to drift of center wavelength of the sensor, displacement of several points can be detected simultaneously. Calibration experiments of several sensors are carried out, in which it could get the conclusions that the sensitivity is about 1.3nm / mm and the linearity is over 0.99. FBG displacement sensors are embedded in the tunnel wall rock symmetrically to monitor precursory information of disaster. In the process of tunnel excavation, displacement increased gradually, and the detecting results had a strong symmetry.