Abstract: This paper introduced the physical properties of reservoir and the completion method of Chengbei and Suizhong 36-1 oilfield. The mechanism of water-sensitive plugging, acid-sensitive plugging, solid particle intrusive plugging, fine particle migration plugging, formation scale deposit plugging, sump oil plugging and formation sand production plugging in water injection wells of two oilfields was studied by cation exchange capacity determination of core, volume flow test, dynamic deposit test and theoretical prediction, the test of the effect of temperature variation on the permeability of water phase, the sensitivity test and on-site water-injection data. The main reasons resulted in plugging in water injection wells of Chengbei oilfield were water-sensitive plugging, sump oil plugging, solid particle intrusive plugging and formation sand production plugging; the reasons for Suizhong 36-1 oilfield were sump oil plugging, solid particle intrusive plugging, formation sand production plugging and scale deposit plugging. This paper provided the basis for choosing plug removal method, developing plug removal agent, choosing scale inhibitor and carrying out plug removal. It had a directive significance for water flooding in two oilfields.