The invention provides a chemically selective mono-methylation method of coumarin catechol compounds, and belongs to the field of natural drug synthesis. According to the method, catechol coumarin compounds are added into an organic reaction system in the presence of a proper amount of alkali catalyst, and high selectivity methylation reactions happen between the catechol coumarin compounds and a methylation reagent so as to obtain a mono-methylation product; wherein the mole ratio of the alkali to the catechol coumarin compounds is 1.0-5.0:1; the mole ratio of the methylation reagent to the catechol coumarin compounds is 1.0-2.0:1, the temperature of the reaction system is -20 to 10 DEG C, and the reaction time is 0.5 to 3 hours. The method has the characteristics of simple operation, mild conditions, good selectivity, and high yield, and can be used to prepare mono-methylation products of coumarin catechol compounds with different substituents.