Backrest assembly of seat, seat and vehicle

The invention discloses a backrest assembly of a seat, the seat and a vehicle. The backrest assembly comprises a main body and a backrest assembly, the back plate is connected with the main body and covers the back side of the main body; the shielding piece is arranged on the inner side of the back plate; wherein the main body can move between a first position and a second position, and when the main body is located at the first position, the shielding piece is completely located on the inner side of the back plate; and when the main body is located at the second position, at least part of the shielding piece is exposed. According to the backrest assembly of the seat, the back plate and the shielding part which are matched with each other to shield the interior of the main body are arranged, so that the interior of the main body is always shielded when the main body moves between the first position and the second position, a good appearance effect is ensured, the overall appearance quality of the seat is impr