Abstract: Based on a comparision between the geological structural features of felsic cryptoex-plosive breccia within granitic basement of No.6722 uranium deposit and the geological effects of underground nuclear explosion, the explosion equivalent of TNT for cryptoexplosive breccia of No.6722 uranium deposit is calculated by a comparision method. The microfissuring optic features, and ultramicrostructure of quartz for cryptoexplosive breccia and basement granite have been studied respectively under the polarization microscope and transmision electron microanalyzer (TEM). The densely parallel directional microfissuring, similar to impact microfoliation (shock lamellae), is observed in quartz grains of cryptoexplosive breccia for No.6722 uranium deposit, but undulatory extinction is not found. It has been found under the TEM that the free dislocations and dislocation walls are sparsely distributed in quartz grains of basement granite, but sharply reduced and even disappeared in quartz grains of granite breccia. The results of a comprehensive study suggest that the cryptoexplosion-forming mechanism of No.6722 uranium deposit is attributed to a brittle deformation due to instantaneous explosion which simultaneously caused the annealing of dislocations; U quartz.