The mathematical expression in the forest and grassland soils to express the general concepts involved in such terms "a soil erosion and soil renewal. " The net addition rate in the forest and grassland soils are represented by an equation of (S rb - S ra ) - (S eb - S ea) == ∫ba R(m, cl, re, b, t) dt-∫ba E(w. r, cl, re, ch, b, t)dt: >=<0 where S, is renewal soil, Se is soil erosion, and variable factors are m =parent material of soil, cl=climate, re=relief or topography, ch=soil characteristics, r=rain or water, w=wind, b=biota, and t = time. Key words: Theoretical analyses, Soil erosion and conservation, Soil renewalil renewal