The correlation Shack-Hartmann wavefront sensor (SHWFS) is widely used in many fields in addition to solar adaptive optics. The requirement for the SHWFS dynamic range increases with the diameter of the telescope, which means a larger detector array is needed. However, the size of the detector would be restricted by the high frame rate needed for the solar observation. To solve this problem, a new, to the best of our knowledge, method called the region-correlation algorithm (RCA) is proposed. In this method, the sub-image array is divided into several regions, and the slopes of sub-apertures are calculated by referring to a selected sub-image in each region. Note that the final slope over a sub-aperture is obtained by combining the relative slopes between the selected sub-image in different regions. The dynamic range in each region is similar to the conventional correlation algorithm, and the final dynamic range of the RCA would be accumulated from those of the regions. The reconstruction accuracy under large aberration would also be improved due to the extended dynamic range. Meanwhile, the RCA does not require any extra device and the increase in calculation time resulting from the RCA is acceptable. The results of numerical simulation and experiment, compared with conventional correlation algorithm, confirm the advantages in the performance of the RCA as well.