Abstract: The method of quickly measuring grain moisture content under freezing and flowing conditions was stuelied. Some basic regularities of measuning grelin moisture content by neutron gauge was obtolined. The conclusions were drawn as follows: the on line measurement of grain moisture content by neutron gauge was a feasible. The different flow speed of grain changed in certain range had little influence on the counting rate R_c of slow neutron. The automatic control of grain dryer could be realized by this on line measurement of grain moisture content by neutron gauge.