The invention belongs to the technical field of biology, and discloses a polypeptide containing two chimeric antigen receptor structures, nucleic acid for coding the polypeptide, a modified T lymphocyte, and a preparation method and application of the T lymphocyte. The polypeptide provided by the invention contains the two chimeric antigen receptor (CAR) structures, wherein one chimeric antigen receptor structure specifically targets a tumor cell, and the other one specifically targets a normal B lymphocyte, so that a CAR-T cell is effectively amplified through recognizing the B lymphocyte ofa blood circulation system, and more CAR-T cells arrive at a solid tumor part so as to specifically kill the tumor cell for improving a treatment effect on the solid tumor. The polypeptide further comprises an ScFv structure of an anti-PD-L1 monoclonal antibody, and the CAR-T cells can simultaneously secrete a PD-L1 monoclonal antibody which interdicts an immunosuppressive action medicated by a PD1/PDL1 signal pathway and T cell failure, so that the treatment effect on the solid tumor is improved, the functional activity of immune cells in vivo is prolonged at the same time, and finally the tumor recurrence is retarded and even avoided.