The invention relates to a method for producing high-octane number gasoline by poor-quality diesel oil. The method comprises the following steps: 1) the poor-quality diesel oil is introduced into a hydrofinishing reactor for a hydrofinishing reaction, a colloid compound, a sulphur nitrogen compound and other impurity are removed in the poor-quality diesel to obtain the hydrofinishing diesel oil; 2) the hydrofinishing diesel oil is introduced into the dehydrogenation reactor for a dehydrogenation reaction, napthene is dehydrogenated and converted to aromatic hydrocarbon, and dehydrogenation product oil is obtained; and 3) the dehydrogenation product oil is introduced into a heavy aromatics lightweight reactor to generate a selective hydrocracking reaction, a heavy fraction is subjected to cycle reaction at the temperature of more than 205 DEG C, and then is completely converted to the high-octane number gasoline. The method can completely convert the poor-quality diesel oil having high napthene aromatic hydrocarbons content to the high-octane number gasoline, and can increase the enterprise economic benefit.