An improved Fourier transform profilometry for the automatic mesurement of 3-D object shapes is presented. Because of using a defocused Rouchi grating to get a qusi-sinusoidal optical field and using grating π-phase shifting technique, the fundarmental spectrum modulated by 3-D object shapes can be extended from 0 to 2f. theorily Cf. is the carrier frequency of the optical field). Consequently,the measurable rate of hight variation can be extended three times more than the unimproved FTP. This article gives the theory and experiment results of the improved FTP.