The imbibition can improve the crude oil production of unconventional reservoirs by the oil-water displacement.Currently，the spontaneous imbibition predominates in the experimental research，which simulates the imbibition process in cores under the capillary force at atmospheric pressure. However，there are fluid pressures during the actual fracturing in the reservoirs，and the traditional experimental methods cannot reflect the forced imbibition characteristics. Taking the argillaceous dolomite of Qianjiang Formation of Qianjiang Sag in Jianghan Basin as an example，this paper designed an forced imbibition experiment based on low field NMR（LF-NMR）technology and studied the imbibition laws at fluid pressures.The results show that according to the T2 pore classification，98.14%-99.49% of the pores in the shale oil core samples are the small holes and medium holes，and the medium holes are the main reservoir spaces. Compared with spontaneous imbibition，the additional fluid pressure makes more use of smaller pores，and the recovery of 5 MPa and 10 MPa forced imbibition is increased by 24.32% and 62.59% respectively. The imbibition causes fractures on the surface of cores with high clay content，increases the contact area，and improves the oil-water displacement efficiency. At the same time，the imbibition can not only improve physical properties but also damage reservoirs.