The present invention provides a method for preparing an ecteinascidin compound and an intermediate thereof, and specifically provides a preparation method for a novel compound QT9, and a method of using QT9 to prepare an ecteinascidin compound. The method provided by the present invention has high reaction selectivity and high yield, the obtained compound is easy to purify, and defects in the prior art that multiple intermediates are oily substances, and the reaction selectivity is poor are solved. The method of the present invention is particularly applicable to industrial production.