The present disclosure provides an all-trans retinoic acid injectable formulation and its application for a preparation of a pharmaceutical product for treating tumor. The all-trans retinoic acid injectable formulation includes all-trans retinoic acid and solubilizers. The apparent solubility of the all-trans retinoic acid is increased from 0.01 mg/mL to 0.1 mg/mL or more. The injectable formulation can reduce the activity of an infiltrated immuno-suppressive cell population within blood or tumor tissue of a cancer patient, and improve immune clearing effects against tumors. It can be applied independently or together with other pharmaceutical products to inhibit tumor growth and prevent tumor recurrence.
