In order to solve the inefficient and invalid circulation between injection and production wells during waterflooding development in Bohai reservoir，channeling path should be managed，and the starch graft copolymer gel has the advantages of low initial viscosity，high gelling strength，good sealing effect and acid and alkali resistance. It plays an important role in the process of large-channel oilfields or ultra-high permeability zones in land oilfields. Experimental study and mechanism of the effect of space size on the gelling effect of the starch graft copolymer were carried out. The results show that the chemical reaction space environment has a great effect on the gelling effect of the starch graft copolymer，and when the space size is larger，the gelling effect is better. In order to ensure the cross-linking reaction of the starch graft copolymer in the core pores，the concentration of the components that obtained by taking the grinding bottle as the gelling environment needs to be increased while taking the viscosity as the evaluation index. In addition，it is necessary to inject pre-slugs and displacement slugs before and after the injection of the starch graft copolymer into the core，and it will contribute to the promotion of cross-linking reactions among the components.