The invention discloses an extraction agent for preparing potassium nitrate with a nitric acid-potassium chloride extraction method. The extraction agent is prepared from isoamyl alcohol, n-butyl alcohol, tri-n-octylaminetri-octyl tertiary amine, n-caprylic alcohol according to a volume ratio of 1 to (0.1 to 0.5) to (3 to 10) to (1.3 to 3). The extractant provided by the invention has a good extraction effect and high selectivity for hydrochloric acid in a nitric acid-potassium chloride reaction system, the hydrochloric acid can be extracted without while not extracting nitric acid, the nitricacid serving as a raw material is saved, the purity of the nitric acid serving as a by-product is improved; the nitric acid prepared by back extraction can be directly taken as a product for selling.