In 1985-1988 at Minle earthquake risk region, Gansu Province, the regular measuring has been carried out by using the method of dipole electrical sounding with current electrode spacing AB=1km, receiver electrode spacing MN=0.95-1 km, central distance of dipole R=5-8 km. The results show: (1)Apparent resistivity ps does not have yearly variation; (2)The ps variation, about 10 days before the M>4.0 earthquakes, is 3-8% in range of 100 km to the observation point.