In order to explore physical characteristics of planosol,through comparing microstructure of albic soil and topsoil under natural forest area,it found that there were a large number of residues of plant root and soil fauna,soil aggregate structure was abundant, porosity was bigger and soil was loose. Because of mechanical effects of tillage,topsoil mixed with a large number of albic soil and soil porosity reduced. The structure thick-ness of albic soil layer was 2-3 mm sheet,only a small amount of soil porosity ranked along horizontal direction,it was not benefit to soil drainage, there was not crops root. The soil structure of illuvial horizon was nuci-form,it formed crack along its structure when it shrunk. About albic soil porosity（0. 050 0-0. 000 2 mm）of soil water holding capacity,topsoil was 16.9%-20.3% ,albic soil layer was account for 67.4%-83.3% of topsoil,illuvial horizon was account for 25.6 %-54.4 % of topsoil. Gravitational water porosity of topsoil was 17.8%-24.4% ,gravitational water porosity of albic soil layer and iltuvial horizon were only in 1.3%-1.8% and 2.4%-6.4% ,it showed that soil permeability was weak. The ineffective porosity of the soil water holding capacity of illuvial horizon was higher clearly than that of topsoil and albic soil layer.%为探究白浆土的某些物理性质，对自然林下的白浆土和耕地白浆土的土壤微结构进行对比分析。结果表明：自然林下荒地白浆土剖面未受到过任何人为扰动，表层土壤中有大量的植物根系和土壤动物的残留物质，土壤团粒结构发达，孔隙量大，土质疏松；表土层向白浆层呈渐进式过渡；而耕地白浆土的表层土壤，由于受机械耕作影响，土层内混有大量白浆层土壤，土壤紧实，孔隙量减少。白浆层土壤结构呈厚度为2～3mm片状结构，仅有少量水平方向发展的孔隙，无利于土壤排水的纵向孔隙，无作物根系；淀积层土壤呈小核状结构，干缩后沿结构形成裂隙。白浆土的土壤总有效储水孔隙（0．0500～0．0002mm）为耕层的16．9％～20．3％。白浆层仅为耕层的67．4％～83．3％，淀积层为耕层的25．6％～54．4％。直径〉0．05mm的重力水孔隙耕层在17．8％～24．4％，白浆层和淀积层土壤的重力水孔隙仅1．3％～1．8％和2．4％～6．4％，表明土壤通透性差。直径〈0．0002mm的无效孔隙，淀积层明显高于耕层和白浆层，土壤持水能力强。
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