The disclosure discloses a method for forming a doped epitaxial layer of contact image sensor. Epitaxial growth is performed in times. After each time of epitaxial growth, trench isolation and ion implantation are performed to form deep and shallow trench isolation running through a large-thickness doped epitaxial layer. Through cyclic operation of epitaxial growth, trench isolation and ion implantation, the photoresist and hard mask required at each time do not need to be too thick. In the process of trench isolation and ion implantation, the photoresist and etching morphologies are good, such that the lag problem of the prepared contact image sensor is improved. By forming the large-thickness doped epitaxial layer by adopting the method for forming the doped epitaxial layer of the contact image sensor, a high-performance contact image sensor applicable to high quantum efficiency, small pixel size and near infrared/infrared can be prepared.