The invention discloses a workpiece sealing structure for tank external electroplating of an engine cylinder block. The workpiece sealing structure for tank external electroplating of the engine cylinder block comprises a workpiece rack and workpieces, wherein a syrup material coats at least one axial end surface of each workpiece; and the workpieces are pressed in the axial direction by the workpiece rack. By the syrup material of which the viscosity can meet the sealing effect, seal of the axial end surface of the cylinder block is formed; the sealing effect can be good in an electroplating process, an electroplating process can be carried out normally, meanwhile, the workpiece sealing structure is easy to clean after electroplating, and therefore, working efficiency is improved; and in the process of electroplating and in the later period, environmental protection of a surrounding environment is guaranteed, and problems that the environment is polluted, the working efficiency is reduced and the quality of electroplating is affected due to materials such as sealant are eliminated.