Three-step spatial quasi-phase-shifting technique is able to demodulate the phase from a single frame of fringe pattern. This technique is suitable for dynamic fringe analysis. An improved three-step spatial quasi-phase-shifting technique is presented in this paper. According to actual situation, the number of pixels and the size of neighborhood are able to be tuned arbitrarily to calculate the phase of each pixel. It is conducive to the noise isolation, the error-propagation prevention, and the accuracy improvement in phase demodulation for dynamic fringe analysis.