The objective of this work is to develop a 3D measuring system for on-line 3D measurement in industry locale. Our system is based on the depth image using a structured-light method. A generator emitting a single stripe light and a camera are used to establish a 3D vision measurement system which is also called as a subsystem. But it only can obtain the depth image of a part at the measured object section. Our system is made up of four subsystems placed symmetrically in space. The depth images obtained by the subsystems are joined to form the depth image of a full section. If the object is uniformly shafted along a fixed beeline direction, the depth image of the full object surface is achieved. The indefiniteness in the image combination criterion can be removed when using the depth image. This paper introduces the system principle and the mathematical model. The algorithm is proposed with system parameters. A prototype is developed. The system has the range of 100mm in height x 100mm in width. The length is not limited. The measuring error is less than 0.5mm in height and width and less than 0.01mm in length. The characteristics make the system suitable for on-line 3D shape measurement and non-contact measurement with high speed.