The dislocation distribution of SiC wafers was studied by lattice distortion detector. The dislocation distribution of the whole SiC wafer or a local area was obtained by scanning the SiC wafers etched by molten KOH. Compared with the scanning corrosion mapping of the LEXT OLS4000 3D laser confocal microscope, the scanning corrosion mapping of the lattice distortion detector can fully display the dislocation etch pit information. According to the color and size of the etch pits, three types of threading dislocations were identified, in which black spot corrosion pits correspond to screw dislocations (TSD), small size white spot corrosion pits correspond to edge dislocations (TED), and large size white spot corrosion pits correspond to mixed type dislocations (TMD). The lattice distortion detector was used to study the dislocation density and distribution of 4-inch (101.6 nm) N-type 4H-SiC crystal at different growth stages. The results reveal that as the crystal grows, the dislocation density shows a gradual decrease trend. The total dislocation density of the wafer in the later stage of growth is reduced to nearly 1/3 of the total dislocation density of the wafer in the early stage of growth. TED occupies the largest proportion in the wafer and decreases the fastest during the growth process. TSD and BPD occupy a small proportion in the wafer, and the density gradually decreases. The results of 0004 rocking curves indicate high crystalline quality and virtually flat basal planes. It is helpful to feed back the information of the propagation and transformation characteristics of dislocation defects during the SiC crystal growth process, so as to guide the improvement of the SiC crystal growth process.