Abstract: An automatic measurement of wall thickness of large shell based on the principle of grating projection and its application in the automatic measurement of conical shell products are introduced.A method of data merging based on coordinate transformation and  unification is used.Through the comprehensive calibration of multiple coordinate systems of the measurement system，the multiple station scanning data is merged precisely.The product comparison analysis and wall thickness detection are completed by the Polyworks Software，and the measurement uncertainty of wall thickness is analyzed and evaluated.It is showed that the automatic measurement method of wall thickness of large shell based on coordinate fusion can effectively improve the detection quality and efficiency of products.

Key words: Grating projection, Automatic measurement, Coordinate calibration, Data merging, Wall thickness of shell