Flatness is an important inspection index in quality control of the production of industrial work pieces.The most widely-used Coordinate Measuring Machine (CMM) technology has a small number of sampling points and low acquisition efficiency.To solve the problem,a non-contact and simple flatness measurement system based on fringe projection technology is proposed.The device projects fringe patterns onto the surface of the work piece under test,and by calculating the phase of modulated fringe images and calibrating the phase/height mapping relationship,the sample points can be efficiently acquired on the full field of the measured plane.The least squares method is used to calculate the ideal plane,and the deviation from this plane is used to calculate the flatness error.Several experiments are conducted,and the results demonstrate that the proposed system can be applied to the flatness measurement of general industrial work pieces with few measurement errors and high repeatability.