An accuracy improving method for composite grating phase measuring profilometry (CGPMP) based on mixed filtering window is proposed. When CGPMP is used to carry out three-dimensional (3D) measurement, the phase-shifting deformed patterns can be demodulated effectively from the captured composite deformed pattern by proper filters. So the selection of the filtering window is very important. By analyzing the characteristics of noises and their different effects on the spectrum components along different orientations, searching for the best filtering window of the spatial spectrum along the two mutually orthogonal directions, a mixed filtering window to improve measuring accuracy is established. Digital simulating results show that the designedly mixed filtering window has better noise suppression than rectangular, triangular, Blackman and Hanning filtering windows. The experimental results show that the measuring error using the mixed filtering window equalizing noise and spectrum leakage is the smallest, and the root mean square error (RMSE) is reduced by 9.64%, and the measuring accuracy is improved effectively.