The surface quality of steel plate can be measured by grating projecti on method,but the accuracy of detecting hole defects is not enough high.In this paper,in view of the above q uestion,a method of hole defects detection based on double projections is proposed.Two line laser arrays are arr anged at equal intervals above the steel plate,and the equally spaced light and dark grating fields are alternatel y projected.The CCD camera separately collects moire images projected onto the surface of the steel plate i n the left and right directions.The phase shift method is used to solve phase information of moire images in the lef t and right directions,and then reconstructs the three-dimensional contour of the left and right directions.Th rough the binarization of moiré background images to locate the projection blind zone or the discontinuous zone, and then the reconstructed three-dimensional morphologies of the left and right directions a re merged,thereby completing the three-dimensional reconstruction of the steel plate and realizing the measureme nt of the hole defect on the steel plate surface.Experimental results show that the thickness measurement accuracy of the steel plate is 0.05mm,and the hole defect measurement accuracy can be improved to 0.1mm.