The invention discloses a torsion-free ring wrong assembly prevention method of an engine piston. The wrong assembly prevention method comprises the following steps: firstly red lead oil is smeared on the inner wall of a cylinder sleeve; then a torsion-free ring to be recognized is horizontally pressed into the cylinder sleeve with a mark facing upwards and stays for a while, the torsion-free ring is taken out, a red lead oil print belt is observed, and if the red lead oil print belt is located on the lower edge of the excircle of the torsion-free ring, a condition that the small circular face of the tension-free ring faces upwards, and the mark is correctly printed is indicated; and if the red lead oil print belt is located on the upper edge of the excircle of the torsion-free ring, a condition that the big circular face of the tension-free ring faces upwards, and the mark is printed on the opposite side is indicated. According to the torsion-free ring wrong assembly prevention method of the engine piston, the red lead oil is uniformly smeared on the periphery of the inner wall of the cylinder sleeve to determine whether a mark of the tension-free ring in the second layer matches a micro-conical surface structure, so that the torsion-free ring in the second layer is prevented from being reversely mounted (the big circular ring face is upward) to cause reverse pumping of machine oil to a piston top, and thus the machine oil consumption increase fault of an engine is avoided.