The invention discloses a method for preparing antithrombotic medicament apixaban. The method comprises the following steps of: obtaining a compound V by performing an amidation-cyclization two-step one-pot reaction on paranitroaniline serving as a raw material and a general purpose reagent 5-chlorine valeryl chloride under an alkaline condition; performing di-chlorination on the alpha-hydrogen of the V by using phosphorus pentachloride; performing a condensation-elimination reaction with excess morpholine to obtain a compound VI; reducing the VI into a compound VII by using sodium sulfide; performing the amidation-cyclization two-step one-pot reaction on the VII and the 5-chlorine valeryl chloride to obtain a key intermediate III; obtaining II by performing a [3+2] cyclization-elimination reaction on the III and another intermediate IV; and finally, obtaining I by performing aminolysis on the II. The method has the advantages that: process design is reasonable, expensive reagent is not used, reaction yield is high, raw material cost is low, and the method is simple and convenient to operate, has no harsh reaction condition, and is easy to perform large-scale production.