Abstract: During the actual measurement, the accuracy of Fourier transform profilometry (FTP) is vulnerable to the hardware and calculation methods, the fringe image preprocessing technique is proposed based on the least square method. The filter design, the phase unwrapping algorithm and influence of system calibration model on the measurement results are discussed. The result shows that, this improved FTP can reduce the errors, which are caused by the sampling shortage, spectrum leakage, spectrum aliasing, phase wrapping and system calibration. The measurement error of the improved method can be controlled within 2%.