This paper targets at b-value which had been researched quite a lot at home and abroad. b-value is determined by stress state and dielectric properties in the theoretical framework. We analyze the variation characteristics of the b-value in the Hetao seismic belt. We select the earthquakes with M_L≥1.5 which occurred in the Hetao seismic belt since 1970,conduct the quantitative detection of the non-uniform temporal change of M_C by using EMR method,and based on the actual situation of seismic activity,set the lower limit magnitude as M_L2.0 to calculate b-value. We calculate and scan the temporal variation of the b-value by using least square method. The results show that there is a good corresponding relationship between the temporal variation of b-value,strong earthquake activity,network distribution and aftershock deletion. We also calculate and scan the spatial variation of b-value by using maximum likelihood. The results show that the spatial difference is possible caused by stress state and dielectric properties.,b-value relies more relatively on the tectonic property. In addition,the sufficient earthquakes samples in each magnitude interval are still a key step to improve the calculation accuracy of b-value.