There were few and small earthquakes occurred in the history in Ren-qiu oil-field area.The water injection began to be made in December 1976 in this area.During the period of eight years before the water injection,no microearthquakes were recorded at all,but three months after the water injection,earthquakes occurred.With the inerease of Water-injecting amount,seismic activity increased.Up to now there have been four felt earthquakes occurred in this area.The features of the seismic activity are:in the period of one to three months after second order difference △²y_i(being positive value) of the water-in-jecting amount reaching a high value,earthquakes occurred;△²y_i was related with seismic energies;the distribution of epicenters was con-troled by the water-injecting well position;b value of the earthquake sequence was 0.65;and both first motion senses and ratio of amplitu-des at a single station were relatively consistent.The preliminary stu-dy shows that rocks of this area are porous rocks and have more frac-tures,and that the water injection made the pore pressure increase and lowered the frictional resistance at fault surface so that the stre-ss accumulated in the oil-field crust was released by earthquakes.