Primary failure of eruption was diagnosed by oral general examination and CBCT. The features of primary failure of eruption, mechanical failure of eruption and indeterminate failure of eruption, especially differentiate points among them were discussed. The case of failure of eruption from right maxillary and mandible was diagnosed definitely by the combined application of oral general examination, experimental tooth extraction and CBCT. Primary failure of eruption is a rare phenomenon, which is difficult to be differentiated from other failure of eruption in the absence of a genetic history. Experimental tooth extraction can improve accuracy of diagnosis.