Research conclusions：From the analysis and discussion it is concluded the fibre light grid transducer can realize long-distance (50m), quasi-distributed, multi-spots and multi-parameter measurement with the high measurement accuracy. It can accurately measure the vertical displacement change of less than 0.1mm (relative to the reference base), and it is suitable for long-term monitoring with the good capacity of electromagnetic interference resistance and can satisfy the requirement of long-term monitoring the post-construction subsidence of subgrade of Zhengzhou-Xi'an Passenger Dedicated Line in moist loess area.