The invention relates to a synthetic method of an anti-tumor medicine, namely N-[2-[[2-(dimethylamino) ethyl] methyl amino]-4-methoxy-5-[[4-(1-methyl-1H-indole-3-yl)-2-pyrimidyl] amino] phenyl]-2-acrylamide (AZD9291) and a key intermediate of the anti-tumor medicine. The synthetic method comprises the following steps: performing Boc acid anhydride protection on 4-fluoro-2-methoxy-5-nitroaniline to obtain 4-fluoro-2-methoxy-5-nitroanilino tert-butyl formate, then reacting with N,N,N'-trimethylethylenediamine to obtain 4-(N,N,N'-trimethylethylenediamino)-2-methoxy-5-nitroanilino tert-butyl formate, then reducing to obtain 2-(N,N,N'-trimethylethylenediamino)-4-methoxy-5-tert-butyl carbamate phenylamine, then completely reacting with acryloyl chloride and directly removing a Boc protecting group to obtain 2-methoxy-4-N,N,N'-trimethylethylenediamino-5-acrylamido phenylamine, and finally reacting with 3-(2-chloropyrimidine-4-yl)-1-methylindole to obtain AZD9291. A process disclosed by the invention is simple in step, relatively high in yield, mild in reaction condition and easy for realization of industrial production.