The invention discloses a detection method for determining group III nitride single crystal surface dislocation type and counting density of different dislocations by accurate positioning of an atomic force microscope, belonging to the semiconductor material quality check field. The aim of the invention is realized by the following steps: a detection region is marked, the atomic force microscope is utilized to test the surface topography of the marked region, a sample is corroded for a plurality of times and the same marked detection region is tested repeatedly by the atomic force microscope after corrosion each time, corrosion rate of each corrosion dislocation pit is obtained by counting after a plurality of times of corrosions and tests, corresponding dislocation type is judged, thus counting density of different dislocations. The invention breaks through the traditional dislocation detection method by a transmission electron microscope, has simple quadrat method, accurate and efficient dislocation type determination, not only can be used in quality check of various semiconductor materials in industry to promote the development of group III nitride base photoelectric devices inphotoelectric industry, but also can be applied to scientific research on film material dislocation corrosion kinetics.