Provided is a crankshaft structure of an engine. The crankshaft structure mainly comprises a crankshaft body with a U groove. A cylindrical connecting rod neck is arranged at the bottom of the U groove of the crankshaft body. Cylindrical main shaft necks protruding outwards are transversely arranged on the outer sides of the two U ends of the crankshaft body. At least one section of inward transition arc is arranged at the two outer side ends of the U bottom of the crankshaft body. At least one hardening layer is arranged on the surface of the cylindrical connecting rod neck and the surfaces of the cylindrical main shaft necks symmetrically arranged on the two sides. The crankshaft body, the connecting rod neck and the main shaft necks are integrally formed in a die-casting manner with nodular cast iron as the raw material, and quenching and tempering are performed on the surfaces of the main shaft necks and the surface of the connecting rod neck to obtain the crankshaft structure. The crankshaft structure has the beneficial effects that the crankshaft structure is reasonable, convenient and reliable to use, resistant to abrasion, uniform in stress and high in transmission efficiency, a crankshaft neck is uniformly stressed in the moving process, it is avoided that non-uniform abrasion to the surface of the crankshaft neck occurs easily, and therefore the transmission effect and the output performance of the engine are guaranteed.