The East African Rift System, as the most famous continental rift and fault zone on Earth, conducts research on the formation of ground fissures within the rift valley, which is of great significance for understanding the active rift process and guiding the engineering construction of the rift valley area. Based on field investigations, trenching, geophysical exploration, and helium isotope detection of ground fissures in the Kenya Rift Valley, East Africa, this article establishes a multi- level structure of ground fissures in the crust and analyzes their formation mechanisms. The results indicate that the study area has a total of 22 large ground fissures, mainly distributed in the rift basin between the eastern boundary fault and two volcanoes. These ground fissures appear on the surface as ruptures and collapses of loose sediments, as well as simple tensile fractures with degassing on the surface of pyroclastic rocks. Resistivity detection shows that ground fissures are extensions of rock fissures in the crust. Based on the characteristics of helium isotopes, a multi- level structure consisting of ground fissures, rock fractures, faults, magma chambers, and the upper mantle has been revealed. Based on this research, combined with the characteristics of crustal deformation and numerical simulation, the formation mechanism of ground fissures in the Kenya Rift Valley can be summarized as follows: mantle upwelling, mantle intrusion, magma chamber expansion, and surface fracturing.