In order to meet the measurement speed requirement when measuring the equivalent thermal focal length of laser material thermal effect based on the Talbot interferometer, a fast algorithm for solving the Moiré fringe angle was proposed. The influence factors of measuring speed by traditional frequency iterative method were analyzed. Based on the similarity of the iterative computing coordinate value and the separability of discrete Fourier transform, the common points of the coordinate points containing decimal are separated from coordinate operation of the spectrum value solution process. The common is filtered by the Fourier transform exponential term, and the different parts are combined operation on the basis of extracting similarity. The 2-D image is reduced to 1-D, and the index items of different parts are limited to the minimal knowable range, which greatly facilitates the use of table-referring and bit-wise operation. The experimental results show that the measurement time with the same configuration computer is reduced from 15s to 0.4s on the premise of ensuring the measurement accuracy, and the measurement speed is increased by 38 times. The application requirement of the equivalent thermal focal length measurement was well satisfied.