Small end bearings are a critical component of reciprocating engines, and the performance of their lubrication performance directly affects engines’ reliability and mechanical efficiency. There are many factors that influence their lubrication. A new type of small-end bearing test rig was developed to reveal key influencing factors and their influence on lubrication characteristics, and a multi-body dynamic model coupled with elastohydrodynamic (EHD) characteristics was built. The model was verified through experiments. In accordance with the orthogonal experimental requirements, the impact of various factors on small-end bearing lubrication characteristics was analyzed, and the results showed that: (1) minimal oil film thickness (MOFT), friction power, and maximum oil film pressure (MOFP) are the major evaluation indicators of small-end bearing lubrication, and the most significant influencing factors are the pin bushings’ clearance, engine speed, and bushing surface roughness; (2) increasing the clearance of the pin bushings can increase the hydrodynamic lubrication percentage and the average thickness of the oil film, but it also reduces the local minimum thickness of the oil film; (3) an increase in roughness can improve the MOFT and enhance its carrying capacity, but may also increase friction power; and (4) high speeds can increase the thickness of the oil film between the piston pin and bushing and improve lubrication status, but it also increases friction power on the asperity contact region, reducing mechanical efficiency. The research results can be used for the design of connecting rod small-end bearings to improve their mechanical efficiency and reliability.