In order to study the oscillating heat transfer enhancement mechanism of the cooling oil gallery of highly-enhanced piston,the oscillatory flow and heat transfer process of engine-oil in the cooling oil gallery of piston were analyzed by the field synergy theory.CFD software FLUENT was used to simulate the velocity field and temperature field distribution of the fluid in the elliptic and the variations of mean field synergy number and cosine value of synergy angle in both two gallery structures under different conditions were obtained.The results reveal that the field synergy principle could well explain the oscillating heat transfer enhancement performance of cooling oil gallery in highly-intensified piston efficiently.The synergy angles at the inner and outer walls of the water droplet oil gallery are smaller than that of elliptic oil gallery,and the mean field synergy number and cosine value of synergy angles of water droplet oil gallery are larger than that of elliptic oil gallery,which indicates that the synergy degree of water droplet oil gallery and its effect of heat transfer enhancement are much better.Using the field synergy theory to guide the structure design of cooling oil gallery of piston will open up a new way to improve the heat transfer enhancement ability of cooling oil chamber gallery.