The pore-scale imbibition mechanism in fractured water-wetted reservoirs has been acknowledged as an efficient tool to enhance oil recovery. Most rock in a natural reservoir is mixed-wetted, but most studies on the pore-scale imbibition process only focused on the water-wetted rock. This paper adopts two mixed-wetted core samples for microspontaneous imbibition experiment, micro-CT scanning, and nuclear magnetic resonance (NMR) test. The results indicate that the pore radius distribution of the segmented CT images is consistent with that of the NMR test. The microimbibition recovery ratio of core No. 34-1 and core No. 64 in the spontaneous imbibition experiment are 27.7% and 58.2%, which agrees well with that computed by the micro-CT scanning image (27.63% and 56.09%). Based on the segmented images, the influences of the Jamin's effect, pore size distribution, and wettability on the microspontaneous imbibition are visualized and quantitatively studied. The Jamin's effect is the important factor that hinders the microimbibition process. The main pore size of imbibition distributes in the range of 1-25 μm. Furthermore, the pore-scale spontaneous imbibition process in a single pore with mixed wettability is investigated and analyzed. The relationships among the contact angle, capillary force, recovery ratio, wettability, and the microimbibition recovery are revealed.