The characteristics and evolution of the imbibition front during spontaneous oil recovery in mixed wetting capillaries are critical for predicting imbibition efficiency in tight oil reservoirs with complex wettability. By establishing a spontaneous imbibition model under mixed wetting conditions, this study investigates the influence of spatially heterogeneous wettability distribution and the degree of mixed wettability on the spontaneous imbibition front distance and the interfacial deformation behavior. The critical condition for achieving efficient spontaneous imbibition in mixed wetting capillarie is identified. A higher water-wetting fraction results in smaller differences in the stabilized static suction front edge distance, achieving optimal oil recovery time more efficiently. Conversely, a larger cosine difference in contact angles between wet and dry sidewalls leads to greater disparities in this critical parameter. By combining simulation data with a fitting formula for static suction front edge distance variations, combined with analytical solutions for the front distance, we can quantitatively characterize the dynamic patterns of front distance changes and interfacial deformation characteristics in mixed-wetting capillary systems. These findings provide theoretical support for efficient and low-carbon development strategies in mixed-wet tight oil reservoirs.