The invention relates to the technical field of copolymerization of propylene and 1-butene in petrochemical industry, and relates to a method for in-situ assisted preparation of a high-butene-contentpropylene-butene copolymer by using nano powder. The method comprises the following steps: a Ziegler-Natta catalyst precursor, a cocatalyst, a compounded external electron donor, nano inorganic powderand liquid propylene are subjected to homopolymerization, the product and butene are subjected to a copolymerization reaction, and therefore the high-butene-content propylene-butene copolymer is obtained. The invention provides a method for in-situ assisted preparation of the high-butene-content propylene-butene copolymer by using the industrialized nano powder; and the invention solves the problems that the obtained copolymer has the low butene content due to particle pastiness and the obtained propylene-butene copolymer has no obvious advantages in performance in a current method. The high-butene-content propylene-butene copolymer prepared by the method provided by the invention has the butene content of more than 5wt% and good impact properties, and can be widely used in the field of industrial injection molding.