This study was conducted in Changting County, Fujian Province, the typical representative area of eroded red soil in Southern China. The internal factors namely ten soil fertility quality factors were selected and the soil fertility quality grade was generated by weighting ten factors based on SPSS. The external factors including soil and water loss intensity, slope and vegetation cover were estimated by 3S technique and field investigation, DEM and TM images, respectively. Mutations were achieved on the base of cusp mutation model constructed by the internal factors and the external factors, and then the relationships between soil fertility quality evolution and soil fertility quality grade, soil and water loss, slope, vegetation coverage were evaluated separately. The following conclusions were drawn from this research: 1) Among 90 soil samples, the numbers of mutational soils and stable soils were 27 and 63 respectively and their proportions took up 30% and 70% respectively. 2) The mutational soils distributed mainly in soil fertility quality grade 1 and 2 (48.15% and 33.33% respectively), very low and low soil and water loss (37.04% and 44.44% respectively), 5-10 degree and 10-15 degree slope (37.04% and 40.74% respectively), vegetation cover >0.4 and 0.3-0.4 (48.15% and 37.04% respectively). There existed very significant correlations(P<0.01)between Δ and soil fertility quality grade, soil and water loss, slope, vegetation cover respectively, and the order of absolute values of Pearson correlation coefficients was soil and water loss > vegetation cover > soil fertility quality grade > slope. Mutation mainly existed in the area where there is high soil fertility quality, low soil and water loss, moderate slope and high vegetation cover. 3) There is a long period during soil fertility quality evolution, and the discrimination of mutation should be based on the stability of intermediate transition. The more benefit would be achieved with less investment when soil fertility quality was mutational, so the treatment of mutational area should not be ignored while ecological restoration and rehabilitation in serious erosion region were took into account.