The basic principle to check light beam collimation with double spiral moiré fringes is illustrated, and the relationship of the characteristic parameters of double spiral moiré fringes and the angle of divergence, i.e. collimation accuracy, is further deduced and analyzed. In the double spiral moiré fringes analysis, the pure moiré fringes are extracted by low-pass filter in the frequency domain at first, and then the characteristic parameter of the pure moiré fringes is extracted. Two methods are introduced to extract the characteristic parameter, one is Fourier transform algorithm, in which the phase information is derived by Fourier transform in turn, and another is spatial phase shift arithmetic, enlightened by the traditional temporal phase algorithm. The problems of re-sampling in polar coordinates and relevant formulae in the two methods are also discussed, and the results of computer simulation are presented. The result shows that the essence of the above two methods is acquisition of the average of the whole moiré fringes trend, and at last the angle of divergence is obtained with a high accuracy. The error of the fringes period of selfimaging is within ±2.8‰.