The low speed two-stroke marine diesel engine is developing continuously towards long stroke, high pressure, high automation, high intelligence, low consumption and low emission. MAN Company designs new ME-B type diesel engine to meet these requirements. Piston crown are one of the most important components of the engine and thermal load analysis is always the focus of research. ME-B piston crown is modified significantly in structure and dimension compared with old design. Finite element analysis is carried out for piston crown of the latest 6S50ME-B diesel engine by using ANSYS software. The three-dimensional model of piston crown is established and the temperature field is obtained. Using the temperature field as the boundary conditions, the thermal stress field and the weak point on the piston crown are found, which may offer theoretical support for further optimization.