To accurately profile transparent elements with parallel surfaces, a method based on least-squares iteration is presented to extract the phase information from multiple-surface interference fringes. According to the principle of wavelength-tuned phase shifting, the least-squares iteration is applied to obtain the actual phase shifts of the different two-beam interference fringes in each frame. Therefore, it allows extraction of front surface, back surface and thickness variation from multiple-surface interference fringes with high precision. The simulation results show that when the phase-shifting error is less than 0.2 rad, the proposed algorithm needs only 10 iterations and reduces the residual phase errors from 0.512 rad (peak value, PV) and 0.103 rad (root-mean-square, RMS) obtained by Okada's algorithm to 0.005 rad (PV) and 0.002 rad (RMS). Its validation is also demonstrated by the experiment of three-surface fringes analysis.