A measurement device for a traction pin of a semi-trailer has a first laser scanner, a second laser scanner and an estimation module. The first laser scanner is installed at the front of a driving direction of a semi-trailer and has a scanning surface parallel to the driving direction of the semi-trailer. The second laser scanner is installed at a side of the driving direction of the semi-trailer and has a scanning surface perpendicular to the driving direction of the semi-trailer. The first laser scanner is at a distance from the ground in accordance with a first predetermined height greater than a maximum allowed height of a semi-trailer to be measured. The second laser scanner is at a distance from the ground in accordance with a second predetermined height less than the maximum allowed height so as to allow the second laser scanner to detect a traction pin of the semi-trailer.