The invention relates to a separation method of unsulfonated oil in petroleum sulfonate, and concretely relates to a continuous extraction separation method of unsulfonated oil in petroleum sulfonate. The continuous extraction separation method of unsulfonated oil in petroleum sulfonate, used for realizing unchanged interface tension of the petroleum sulfonate obtained after extraction separation, is provided to overcome the defect of interface tension rising of the petroleum sulfonate obtained after extraction separation. The method comprises the following steps: pumping petroleum sulfonate and water into a first-stage mixing and clarifying extractor according to a mass ratio of 1:0.5-1:2, clarifying, separating primary unsulfonated oil and an aqueous soltuion of primary petroleum sulfonate, pumping the aqueous soltuion of primary petroleum sulfonate into a second-stage mixing and clarifying extractor, separating secondary unsulfonated oil and an aqueous soltuion of secondary petroleum sulfonate, and dehydrating the aqueous soltuion of secondary petroleum sulfonate to form a final product. The method has the advantages of simplicity, low cost, and effective separation of highly-equivalent oil-soluble petroleum sulfonate, the interface tension of the finally obtained petroleum sulfonate is unchanged, the oil displacement effect of the petroleum sulfonate does not decrease, and the separated unsulfonated oil can be reused.