Aiming at the problem of limited axial range of differential confocal microscopy (DCM) 3-D measurement method, this study proposes a method to expand the range of DCM (differential confocal axial range expansion method based on double fuzzy, DFDCM). The DFDCM enables range expansion by combining layer scanning with DCM. The problem of effective data fusion in each DCM is solved by using double fuzzy ranging. Then, since only three images are required in each DCM, i.e., pre-focus image, reference plane image, and post-focus image, DFDCM can be well adapted to most DCMs. Quantitative evaluation experiments using the parallel object DCM system show that DFDCM can effectively extend the measurement range of DCM. Under a $10\times $ /0.25 objective, the axial distance between two adjacent reference surfaces is $14 \mu \text{m}$ . In the experiment of step measurement of $28.91 \mu \text{m}$ , the measurement error is $0.392 \mu \text{m}$ and the error rate is 1.34%.