After years of water injection development, the oilfield has entered an extremely high water cut stage, with problems such as increased water injection pressure and poor development effectiveness. In order to solve this problem, this paper analyzes the content and particle size distribution of clay minerals by using target cores, and conducts high power water injection experiments combined with two-dimensional nuclear magnetic resonance technology to study the change rules and reasons of reservoir physical properties. The experimental results show that core 8-2 and core 16-1 are respectively identified as medium sandy fine sandstone and silty sand medium sandy fine sandstone by laser particle size test, and their clay minerals contents are 2.41% and 2.57% respectively; As the water injection ratio increases, the nuclear magnetic porosity exhibits a pattern of first decreasing and then increasing; As the injection rate increases, the permeability (water) fluctuates, with a significant decrease in the early stage and a brief increase in the later stage before continuing to decrease; The damage in the early stage of water injection mainly occurs in medium and large pores, and the damage degree of 8-2 is greater than that of core 16-1; The variation pattern of free water signal in the nuclear magnetic two-dimensional spectrum of the core is consistent with the variation pattern of pore signal intensity in the nuclear magnetic T2 spectrum. Research shows that under the scouring effect of water during water injection, particles and clay minerals in cement are easy to fall off and migrate to the pore throat to block, causing certain damage to the pore throat to reduce permeability (water), so water injection wells have problems such as difficulty in water injection and increase of water injection pressure, which affect the oilfield development effect.