According to the structure of sealing device for stern shaft tube of conventional commercial cargo ship, the problems and out-of-tolerance reasons of centering installation of sealing device for stern shaft tube are analyzed. Combined with the dynamic shafting operation condition, the improvement measures of centering installation process of sealing device for stern shaft tube of conventional commercial cargo ship are proposed, which can adjust the shaft sealing eccentricity of sealing device for stern shaft tube to the static allowable value and ensure the normal shafting installation.