Neutron monitor (NM) in Yangbajing Cosmic Ray Observatory mainly detects nucleus components with energy in a range of 500 MeV20 GeV and a small number of negative muons. On the basis of synchronous data of neutron monitor and atmospheric electric field during 62 thunderstorms from 2008 to 2010, obvious changes of NM counting rate during 27 thunderstorms with significance greater than S5 are found, and among them, 13 cases with significance greater than S10 . A coincident approximate change trend is found between counting rate change percentage and atmospheric electric field amplitude for 13 cases with significance S10 . However no obvious coincident change trend is found for 14 cases with significance 5 S10 . Obvious changes of counting rate do not occur when thunderstorm is just over electric field mill, however obvious changes occur when electric field mill is not exactly below thunderclouds but in the control of bottom positive charge layer. Dorman put forward the theory that NM counting rate changes are correlated with the atmospheric electric field, thus they attributed the former to the acceleration of the electric field to negative muons inside thunderstorms. However, there is found no evident correlation between NM counting rate charge and the atmospheric electric field in this paper, so our experiment does not support Dormanetal's theory.