利用Master sizer2000激光粒度仪对所采样品进行粒径分析，分析了土壤粘粒组、细粉粒组、粗粉粒组、中值粒径和平均粒径沿剖面的变化情况。通过分析得出剖面特征为：发育浅薄的白云岩剖面粘粒组和细粉粒组随剖面加深而逐渐减少；发育程度相对较深的灰岩剖面，粘粒含量随剖面加深而增大，在某一位置达到最大值（JGA为184cm，JGB为285cm），随之粘粒含量又随剖面而减小。鸡公剖面和华蓥剖面，剖面粒度以5~50μm的粗粉粒级为主体，含量分别是38.68%~48.09%和53.12%~59.99%。中值粒径和平均粒径具有相似的变化曲线，随剖面加深，粒径整体增大。 通过矿物学分析结合化学分析，研究了粘土矿物含量、pH值CaCO3含量在剖面的变化规律，即剖面从下向上，表征发育高级阶段的粘土矿物含量增高，如蒙脱石和伊利石。其他粘土矿物也是从无到有；pH值CaCO3含量随剖面向上呈减小趋势。

The characters of karsts soil are four: (1) soil layer is thin and the soil is barren; (2) the soil is not continuously distribution and separated by the stone-teeth; (3) water and soil resources are separated; (4) slopping field is more, the flat is few. The ecological environment is extremely frail in karsts area. The soil in karsts is the base of the local agriculture. In this dissertation, 6 profiles are chosen as the object of study. Three of them are the weathering profiles of limestone in Beibei region, Chongqing. Another three are the weathering profile of dolomite in Huaying region, Sichuan. Soils were collected 52 samples and 6 samples of bedrock. In this paper, the variation of the clay fraction, the coarse silt fraction, the fine silt fraction, the sand fraction, median size and average size along the section were analyzed. The contents of clay fraction and fine silt fraction decreased along the dolomite profile which developed poorly. For the better developed limestone profile, the clay content increased along the profile up to the most value at one location; then it decreased along the profile. For the JGA profile, the location was 184cm, and the location was 285cm for JGB. The coarse silts which is 5~50μm were main composition for all JG and HY profile, they were 38.68%~48.09% and 53.12%~59.99%, respectively. The mean size increased along the profile with similar tendency to median size. That the clay sizes of soil were leached by rainfall was a key reason to that distribution. In this paper, the content of the clay mineral, the pH, and the calcium carbonate were dealt. The results showed that the clay mineral rose up with the increasing of depth, such as montmorillonite and illite. Other mineral gradually appear. The contents of the pH and calcium carbonate have the decreasing trend. This study shows that grain size curves of the acidic insoluble material from parent rock and overlying weathering soil are consistent with each other and are of gradually changing characteristics, which indicate that the weathering soil inherits and comes from bedrock. The remarkable volume decrement will happen during the pedogenesis processes in virtue of the low content of insoluble residues of carbonate rocks, so it is a non-isometric weathering process. During the process soil particles can be transported into the underground spaces. So the soil can disappear from the land surface by dropping into gaps and/or caves without long-distance transport. Sequentially, soil loss will occur by short-distance displacement without human activity, and soil will become more uneven in distribution on the land surface.