In order to take effective copyright protection for 2D engineering drawings，the paper presents a reversible watermark embedding algorithm based on difference expansion for 2D engineering drawings. The algorithm works on the feature of poor relevant of vertex coordinates of lines in engineering drawing

embedding watermark information by modifying the vertex coordinates of lines. Because of minute revision

there isnt any visual redundancy. During information extracting

the algorithm can restore the original engineering drawing accurately

and meets the requirements of high-precision machining

and also realizes the blind extraction. The experimental results show that the algorithm achieves good results

and easy to implement

it can be applied to the copyright protection of engineering drawings

content certification

information secret transmission and other fields.