The deep fissure zones have been discovered during the engineering investigation at Pusiluo dam-site, Yalongjiang River. The zones, located 100-200 meters beneath the ground, are separated by thick uninterrupted rock mass between the ground gravity unloading zone and the fissure zone. The occurrence of the deep fissure zone is similar to that of a group of NE directional faults in this area. The newest fault gouge was developed 27-90 thousand years ago and had horizontal, oblique, up-down scratches on the fissure surface. All these observable facts indicate that the deep fissure zone was perhaps caused by the recent activity of the faults,  which generated seismi waves and created the deep fissure zone when the stress of waves was larger than rock's tensile strength. The genesis of deep fissure zone has been observed in the ground nuclear explosion and rock dynamics experiment.