The invention discloses a three-dimensional measurement system and three-dimensional measurement method for a steel plate with lasers and vision combined. The system is mainly composed of two background projectors, a total station, a three-dimensional scanner and a GPU server. The background projectors, the three-dimensional scanner and the total station are all connected to the server. The method comprises the steps that a plurality of laser labels are placed around the steel plate to be measured; the lasers are used for measuring the three-dimensional coordinates of the labels, and two cameras in the three-dimensional scanner are used for shooting the laser labels; an HOG and an SVM are used for detecting the original positions of the labels; a DOG is used for precisely locating the center of the labels; the three-dimensional coordinates of the labels are measured, the coordinates are converted into a laser coordinate system from a visual system, the errors of a calculation sum are obtained, and an error field is constructed; the scanner is used for measuring the steel plate to be measured to obtain the three-dimensional data of the steel plate; the error field is used for correcting the three-dimensional data of the steel plate to obtain the more accurate three-dimensional data of the steel plate. Laser measurement and vision measurement are combined, and the errors of the vision measurement can be greatly reduced.