The invention discloses a laser calibration method for realizing non-contact measurement on the size of a workpiece to be measured and particularly relates to online measurement on sizes of industrial assembly line products. The scheme provided by the invention is that the laser calibration method comprises the following steps of: clamping two lasers on a bracket, enabling light emitted by the two lasers to be parallel and calibrating the distance between the two lasers; transmitting the laser light to a workpiece to be measured to form two light spots; acquiring an image of the workpiece to be measured by using a CCD (Charge Coupled Device); extracting the quantity of pixels between two light spots in the image and the quantity of overall dimension pixels of an object to be measured by using an image processing algorithm in matlab; and solving a scaling factor according to the known actual distance between the two light spots in the image and further solving an overall dimension parameter of the object to be measured. According to the measuring method provided by the invention, a standard gauge block is not needed to be calibrated; the distance and position relationship between the CCD and the object to be measured is not strictly limited; field mounting is conveniently realized; and the measuring method is suitable for online measurement of the industrial assembly line.