Identification of microcracks in time is important for the safety control of concrete structures. In this study, four-point bending experiments were conducted on basalt fiber concrete specimens. The strain fields information on the specimen surface were acquired by digital image correlation technique during the loading process. In the horizontal strain field, 300 points with large strains were selected as points of interest (POI), the aggregation factor was calculated based on the standard deviation of the coordinates of the POI in the strain field, and a method for identifying microcracks associated with a single strain field only was proposed by using the distribution evolution of the aggregation factor during the loading process. This method can exclude the error generated by human judgment of microcracks, but it is not sufficient to identify multiple microcracks. The accuracy of the method exceeds 95% and is suitable for engineering applications.