The invention discloses a cylinder head assembly. Five cylinder head support lugs are arranged at the outer edge of the top surface of a cylinder head and each cylinder head support lug is provided with a screw hole; five cylinder cover support lugs are arranged at the outer edge of the bottom of a cylinder head cover and each cylinder cover support lug is provided with a via hole; five positioning support lugs are arranged at the outer edge of a sealing gasket and each positioning support lug is provided with a positioning hole; a screw passes through the via holes of all the cylinder cover support lugs on the cylinder head cover and the corresponding positioning holes on the sealing gasket and is screwed in the screw holes of the corresponding cylinder head support lugs to fix the cylinder head cover, the sealing gasket and the cylinder head together. Since the sealing gasket, the cylinder head and the cylinder head cover are fixed together tightly, the position of the sealing gasket is fixed relatively, the generation of a gap can be avoided effectively when the sealing gasket is pressed to deform; and distances between the screw holes of every two adjacent support lugs of the five cylinder head support lugs of the cylinder head are set to be consistent basically, therefore, even strength for each stressed part can be ensured after assembly, and the sealing gasket can achieve good stressed deformation effect, which is beneficial to improving the sealing performance.