The invention provides a device for measuring the telescoping displacement of an underground telescoping hollow mechanism. The device comprises a PC terminal, an overground module and an underground module. The PC terminal is connected with the overground module which is in communication connection with the underground module. The underground module is installed in the telescoping hollow mechanism. The PC terminal and the overground terminal achieve control and modulation of emission signals, and conditioning, mixing filtering, acquisition processing and range finding display of receiving signals together. The underground module and the telescoping hollow mechanism synchronously telescope, thereby achieving signal laser emission, receiving and photoelectric conversion during displacement measurement. According to a method and the device for measuring the telescoping displacement of an underground telescoping hollow mechanism, control and measurement of telescoping displacement of an underground telescoping hollow mechanism can be achieved on the ground; working states of the telescoping mechanism can be monitored in real time; and effective data is provided for safety and quality evaluation of project construction.