When atmospheric turbulence coherence length r0 is measured by traditional Differential Image Motion Monitor(DIMM) method, it is difficult to obtain a stable r0 value due to limitation of light spot pairs. Therefore, this paper proposes a statistical method to increase the statistical number of light spot pairs from one on a wavefront to twelve aligned in a square, and completes the statistics on a SHWFS light spot array captured by the Shack-Hartmann wavefront detector. The method spatially increases the statistical number of samplings and the spatial symmetry of r0 measurement, so it decreases the statistical time greatly. The experiments show that only three hundred of wavefront samples gotten in 300 ms are enough to obtain the r0 with a variation less than 3%. The presented method solves the large error problem in the traditional r0 measurement for long time, and has contributed to the improvement of imaging accuracy of adaptive optical systems for ground-based telescopes