In order to solve the problems of high water content, low production rate and low oil recovery in the middle and low permeability reservoirs of Shengli Oilfield, a capillary imbibition displacement model was designed, by combining capillary imbibition displacement experiments with core displacement experiments, and taking into account the parameters of capillary inner diameter, microbial liquid concentration, wettability, core permeability, and crude oil viscosity, the characteristics and influencing laws of microbial imbibition and displacement in the middle and low permeability reservoirs were revealed. The research results show that the larger the capillary inner diameter, the better the imbibition effect. The influence of different microbial liquid concentrations on the imbibition process shows significant difference and there is an optimal concentration range. One important factor promoting capillary imbibition is that the microbial liquid changes the capillary wettability through adsorption during the imbibition process. In the actual field applications, uncentrifuged bacterial liquid can be directly used for microbial flooding operation. The microbial liquid concentration, crude oil viscosity and core permeability all affect the microbial liquid displacement effect. As the microbial liquid concentration increases, the oil recovery first increases and then decreases. The higher the core permeability, the better the microbial liquid displacement effect. The higher the crude oil viscosity, the smaller the microbial liquid displacement effect. The research results can provide theoretical support for the practical application of microbial flooding technology in middle and low permeability reservoirs.