A calibrating method for the scanning direction of 3D measurement system based on linear-structure light using a plane calibration board is proposed. In the calibration, the camera′s inner parameters are calculated with the plane calibration board first. Then the plane calibration board is placed on a position, the 3D sensor moves along the scanning direction and collects pictures at the same time. The outside parameters of the camera for every position of the 3D sensor are worked out. With these pictures and the camera coordinates of homologous points on each picture can be worked out with the inner and outside parameters. At last, linear equation is acquired by linear fitting with the camera coordinates of homologous points. The scanning direction is equal to the direction of the line. The experimental result shows that the method has high precision and it is practical in 3D measurement.