Abstract: A novel composite grating based on flat mage modulation is proposed to enlarge the measuring range of the Fourier transform profilometry (FTP). A sinusoidal image and a flat image without stripes are modulated into the grating to restrain the zero component in the Fourier spectrum. Compared with the composite grating based on the phase-shifting technique, the spectrum of the proposed grating becomes simpler because only DC component is introduced by the flat image. So the modulated information is easier to be filtered and the measuring accuracy is improved. The intensity calibration of the flat image demodulated from the composite grating is simpler than the sinusoidal image because only mean value calibration is involved. Moreover, the intensity of the demodulated flat image is proportional to the reflectance of the measuring object, which has some application in the practice. The Matlab is used to simulate the proposed method, and the experiment is performed to verify the feasibility of the proposed grating. Both of them demonstrate the flat image can be used to restrain the zero component and enlarge the measuring range of the FTP, and the measurement accuracy is improved.