Abstract: An interval inversion method was proposed to retrieve phase information directly from single interferogram. Due to the sign ambiguity of inverse cosine, an inversion was needed in the phase interval of (,2). This interval estimation was translated to a problem of fold-line fitting that can be solved by a genetic algorithm. Further, the least square was employed to find an optimal linear carrier frequency for the final phase distribution. The method was applied to one-dimensional and two-dimensional numerical examples. Simulation results, compared with the methods of traditional Fourier transform and fringe analysis, demonstrate the effectiveness and the ease of use.