In order to solve the oscillatory heat transfer problem of gas-liquid two-phase flow of cooling oil gallery of piston, a reciprocating oscillatory experimental device reformed by diesel engine was designed and established. The oscillatory flow process of gas-liquid two-phase flow in a test piece was visualized by high-speed camera technology, and the oscillatory flow patterns of gas-liquid two-phase flow in the test piece at initial and full oscillation stage under different rotation speed and liquid filling rate were analyzed respectively. The results show that at initial oscillation stage, the interface between gas and liquid is obvious, and there is no intense turbulent mixing motion. At full oscillation stage, the movement law and flow pattern of liquid change periodically. Rotational speed mainly affects the turbulence intensity of gas-liquid two-phase flow, while the liquid filling rate mainly affects the flow pattern of gas-liquid two-phase flow. The research results reveal the oscillatory flow rules of gas-liquid two-phase flow in cooling oil gallery, and also provide a reference for the structural optimization design of the highly-intensified piston in the future.