In order to solve the problem of injected fluid channeling caused by large-size advantage channels in offshore oilfield，the basic performance evaluation，plugging rate，multi-stage plugging and increasing oil and decreasing water effect of three plugging agent was studied through experiment and mechanism analysis taking reservoirs and fluid of Bohai Oilfield as the research object. The results show that the plugging agent BH-1 is a viscous fluid before solidification and has good injectivity. After curing it is a kind of gray-black dense solid，whose curing time ranges from 24 h to 120 h. It has high solid compressive strength and abrasion resistance，which is suitable for plugging large-size advantage channels near wellbore area. Before gelling，the gel with semi-interpenetrating network structure is a kind of viscous fluid with favorable injectivity. After waiting on cementing for 24 h in the pores of core，the mixture began to appear obvious cross-linking reaction and became to form the“mesh”molecular aggregates after 120 h，and the colloid has the characteristics of high compressive and erosion resistance，whcih is suitable for the plugging of large-size advantage channels in the deep reservoirs.After all the high-permeability core holes were plugged，the Cr3+ polymer gel flooding can improve the swept effect of matrix in low and high permeability cores，and the oil recovery was increased by 29.4%，while the oil recovery was only 13.1% when the plugging distance is 50% of the total plugging distance. Therefore，the plugging distance of the large-size advantage channels in Bohai heavy oil reservoirs should be more than 50% of the injector-producer distance. From the technical and economic point of view，the plugging agent consists of multi-stage combination of slugs，and the injection order is：Cr3+ polymer gel（about 50%），the gel with semi-interpenetrating network structure（about 35%），plugging agent（about 15%）.