Abstract: The ground fissures in Longyao County are the typical surface disaster in North China region. They not only caused eroding, collapsing, extension fracturing, faulting, cracking and other geological disasters on the earth’s surface, but also caused severe economic losses in the local agricultural production, engineering construction and the lives of the people. This paper aims to reveal their genetic nature. It is based on geological investigation, monitoring and measuring, trenching, physical exploration. It studies the development characteristics of the Longyao ground fissures. They include the planes, profiles, deep and activity aspects. The paper summarizes the laws of ground fissures. Finally the ground fissure mechanism is analyzed from their crack-pregnant environment, crack-opening conditions and cracking process.the study concludes that: (1)Longyao ground fissures expose in a dozen villages of more than 30km long. They extend towards NWW and NEE which are concordant with the direction of Longyao fault system. Their periodicities are consist of opening, closing, slowly cracking and suddenly cracking periods.(2)Longyao ground fissures are controlled by the faults zone. The conditions such as deep structure, faulted structure and structural landform provide the ground fissures with crack-pregnant environment in the area. The crack-pregnant environment has through three stages: stress accumulation and fractured zone formation.(3)Faulting is the foundation of ground cracking. The groundwater exploitation and surface infiltration also are the important factors.(4)the process of Longyao ground fissures is heterogenous temporally and spatially. From the present investigation and study, the ground fissures are in active period in the area.