In order to study the relationship of oildriving efficiency with microcosmic pore structure in the Changyuan ultralow permeability reservoir of outer edge of Daqing oilfield, the CT technology was used to research dozens of natural cores. Lots of data such as pore radius, throat radius, porethroat ratio, coordination numbers, tortuosity and shape factor were obtained. The waterflood experiment was conduct and each oildriving efficiency was recorded, then the effect of pore structure parameter on oildriving efficiency was studied. After the standard processing, the linear regression equation of pore structure parameters and oildriving was obtained. The results showed that, among all the parameters, the average throat radius was the critical element with a factor of 0.531. While the average pore radius was considered to be insignificant with a factor of 0.045.