The invention relates to an externally applied medicinal oil for treating solar dermatitis, and a preparation method thereof. The externally applied medicinal oil comprises a medicinal component and an oily matrix, and the medicinal component comprises 1-20 parts of pearl powder, 1-10 parts of calcined gypsum and 1-10 parts of calcined Concha Margaritifera; and the oily matrix includes white sesame oil, or camellia oil, or white sesame oil and camellia oil mixed oil. The preparation method of the externally applied medicinal oil comprises the following steps: crushing the medicinal raw materials to prepare fine powder; and adding the oily matrix according to a solid-liquid ratio of 1:(8-10), immersing the fine powder at an oil temperature of 80-120 DEG C for 12-48 hours, and filtering the obtained mixture, and taking obtained oil to prepare the externally applied medicinal oil. Experiments prove that the medicinal oil has an obvious curative effect on the solar dermatitis, and has the advantages of quick effect, short treatment course, low cost, simplicity in preparation, and no side effects.