【Objective】Bulk density and pore distribution characteristics are two fundamental soil properties. However, not much has been reported about physical properties of soils containing rock fragments and influences of rock fragments in soil on bulk density and formation of non-capillary porosity of the soil. Purple soil is the major type of soil in the Three-Gorge Reservoir Region and the high content of rock fragments is one of the important characteristics of the purple soil. The existence of plentiful rock fragments in the soil will sure affect the formation of bulk density and porosity characteristics. The purpose of this study is to understand how rock fragments affect bulk density and porosity characteristics and its possible mechanism in the purple soil of the region. It is expected that the findings in this study may help collect some basic parameters of soil spatial distribution for building models to be used to predict spatio-temporal variation of surface runoff and soil erosion, while providing some scientific bases for irrigation and water management of agricultural land in mountainous areas. 【Method】In order to explore in depth and evaluate potential effects of rock fragments on bulk density and porosity characteristics, soil samples typical of the soil were collected during field surveys for in-lab analysis of contents and fractions of rock fragments in particle size, soil physical properties, bulk density and porosity. 【Result】(1) Rock fragments varied sharply in density, porosity, saturated water content, and weathering degree. The larger in size, the lower in weathering degree, the higher in density, and the lower in porosity and saturated water content. The three fractions of rock fragments, small, medium and large, were 1.9, 2.2 and 2.3 g cm^-3 in density, 0.16, 0.10 and 0.06 cm³cm^-3in porosity and 8.0%,4.5% and 3.2% in saturated water content (mass moisture content), respectively. (2)Content of rock fragments was closely related to total bulk density and bulk density of fine earth. With increasing rock fragment content, total bulk density increased while bulk density of fine earth decreased, showing a linear negative relationship. (3) Soil pore distribution was closely related to content of rock fragments. With increasing content of rock fragments, total porosity and capillary porosity of the soil decreased while non-capillary porosity, i.e. macrospore, increased.【Conclusion】The sum up, rock fragments, especially those small in size, have certain water holding and supplying capacities. In farmlands under water stress, rock fragments can also release some water available for plant growth. The existence of rock fragments in the soil helps improve soil structure and soil water permeability.