A method for performing contactless ODEP for separation of CTCs is provided with the steps of obtaining patients' blood with rare cell suspected CTCs; adding at least one fluorescent antibody binding to CTCs into the blood; staining the blood; injecting the stained blood with fluorescent dye into an ODEP device and then performing fluorescent image identification; trapping the CTCs with at least one fluorescent antibody in the ODEP device by creating an image pattern and then generating an ODEP force; Separating the trapped CTCs from other non-CTCs cells; absorbing the trapped CTCs; and obtaining a high purity of CTCs. An apparatus for performing contactless ODEP for separation of CTCs is also provided.