A computer-implemented method for calibrating external parameters of an image acquisition device which is provided on a body side of the vehicle, and a field of view of which is downward, and a calibration plate being arranged on the ground at the side of the vehicle and being within the field of view of the image acquisition device, the method comprising: acquiring (S101) an image captured by the image acquisition device; determining (S102) a plurality of marking points on a calibration plate in the image; determining (S103) a first conversion matrix from an image pixel coordinate system to a calibration plate coordinate system based on coordinates of each of the marking points in the image pixel coordinate system and the calibration plate coordinate system; determining (S104) a second conversion matrix from the calibration plate coordinate system to a vehicle body coordinate system based on coordinates of at least one wheel grounding point of the vehicle in the calibration plate coordinate system and the vehicle body coordinate system; and determining (S105) external parameters of the image acquisition device by using the first conversion matrix and the second conversion matrix, wherein, the coordinates of the at least one wheel grounding point in the calibration plate coordinate system are determined by: determining (S301) the coordinates of two wheel grounding points on one side of the vehicle in the calibration plate coordinate system; and determining (S302) the coordinates of two wheel grounding points on the other side of the vehicle in the calibration plate coordinate system by using the determined coordinates and a vehicle model of the vehicle. acquiring (S101) an image captured by the image acquisition device; determining (S102) a plurality of marking points on a calibration plate in the image; determining (S103) a first conversion matrix from an image pixel coordinate system to a calibration plate coordinate system based on coordinates of each of the marking points in the image pixel coordinate system and the calibration plate coordinate system; determining (S104) a second conversion matrix from the calibration plate coordinate system to a vehicle body coordinate system based on coordinates of at least one wheel grounding point of the vehicle in the calibration plate coordinate system and the vehicle body coordinate system; and determining (S105) external parameters of the image acquisition device by using the first conversion matrix and the second conversion matrix, wherein, the coordinates of the at least one wheel grounding point in the calibration plate coordinate system are determined by: determining (S301) the coordinates of two wheel grounding points on one side of the vehicle in the calibration plate coordinate system; and determining (S302) the coordinates of two wheel grounding points on the other side of the vehicle in the calibration plate coordinate system by using the determined coordinates and a vehicle model of the vehicle. determining (S301) the coordinates of two wheel grounding points on one side of the vehicle in the calibration plate coordinate system; and determining (S302) the coordinates of two wheel grounding points on the other side of the vehicle in the calibration plate coordinate system by using the determined coordinates and a vehicle model of the vehicle. <EOS>