The effect of foundation reinforcement is closely related to the change of water content in soil during vacuum preloading.The traditional test method of the water content is model test in the laboratory.This paper introduces the neutron soil moisture meter into the field test of water content during vacuum preloading construction.The instrument calibration is carried out through the indoor test for field borehole soil sampling,and then the water content of soil during vacuum preloading is studied.Based on the laboratory test data of oven drying method and the neutron soil moisture meter test data before and after foundation reinforcement,the test precision of the neutron moisture soil meter is studied.The variation law of soil water content with vacuum preloading time at different depths is obtained,and the influence mechanism of vacuum load on soil water content is analyzed.The test method is simple and convenient,and the result accuracy is reliable.