Disclosed are a reticulocyte growth factor (RGF), and preparation method and application thereof. The present invention separates and purifies the factor from the impurity of an α1-antitrypsin formulation (from human plasma), and determines that the factor is a fragment in the precusor of an α1-antitrypsin molecule, and has a powerful function of promoting reticulocyte production in mice. The RGF of the present invention can be prepared into drugs for treating serious anemia.