Abstract: A longitudinal calibration method was proposed for welding pool altitude measuring system for tungsten inert gas welding,based on Fourier transform profilometry (FTP).A sinusoidal grating was projected to the calibration panel located in the welding pool,and the panel was longitudinally driven by a one-dimensional precise moving apparatus to construct diverse altitudes.A 4f optical system transferred the grating fringes on calibration panel to the output plane,on which a white screen was placed to receive the output image and grating fringes captured by a CCD.The phase value at each point on pixel plane was obtained by digital image processing,and then the relationship between phase value and welding pool altitude was determined.The distribution of welding pool surface height was acquired through the longitudinal calibration of measuring system and subsequent welding experiments.