【Objective】Papers available in the literature show that loess dust precipitation exists generally in North China, becoming an important source of topsoil in the region. It brings in a large amount of fine mineral particles and nutrient elements, especially, CaCO₃, to the soil. CaCO₃ is an important component of the soils in arid, semi-arid and semi-humid regions, and hence a major indicator reflecting development degree of a soil. The purpose of this paper is to study vertical distribution of CaCO₃ content and its characteristics in the mountainous soil of North China, in an attempt to explain causes of this phenomenon from the perspective of soil genesis. 【Method】A total of 257 soil profiles of various soil series in Beijing and Shanxi Province were investigated for mechanical composition, CaCO3 content and lime reaction and statistic analysis was performed of the data. On such a basis, vertical distributions of CaCO₃ content and lime reaction in the mountainous soils of North China and their characteristics were summarized, and causes of the phenomena explained with the theory of soil genesis.【Result】Results show that the topsoil in North China is mainly composed of silt, which is similar to loess, indicating that loess dust precipitation is an important source of soil minerals, bringing in CaCO₃ to the topsoils of the mountainous soils in North China. As soil humidity varies sharply from area to area due to difference in elevation, soil CaCO₃ content does too. In areas above 1 500 meters in elevation, the soils are quite high in humidity (varying in the humid and damp regime)_due to relatively high precipitation (mean annual precipitation of over 600 mm) and relatively low temperature (varying in the gelic or cryic soil temperature regime), and good to vegetation, which in turn reduces surface runoff, but enhances downward leaching of CaCO₃. As a result CaCO₃ is leached out of the soil, no matter what it is derived from, and no lime reaction is detected throughout the solum. So in these areas, bio-climatic conditions play a leading role affecting soil CaCO₃ content and lime reaction. However, in areas ranging between 500 and 1 500 meters in elevation, the soils are relatively low in soil humidity (varying in the semi-arid-humid/humid regime) due to relatively low precipitation (mean annual precipitation of < 600 mm) and higher soil temperature (varying in the frigid/temperate regime), and hence not so good to vegetation, As a result, CaCO₃ leaching is weakened and lime reaction could be found almost everywhere. Therefore in these areas bio-climate conditions descend from the leading role to a major role, following behind the role of parent material. Whatever, no obvious characteristic of the distribution of soil CaCO₃ content and lime reaction could be summarized in areas below 500 meters in elevation.【Conclusion】In conclusion, the characteristics of the vertical distribution of soil CaCO₃ content / lime reaction caused by leaching process, strong or weak, is one of the typical soil genetic characteristics of the mountainous soils in North China.