The soil microbial biomass carbon and nitrogen were measured in three long-term expenments,the different vegetation remediation experiment in red earth ecosystem, the experiment of red earth highland with different fertilization systems and the pollution experiment of Pacloutrazol and Chlordimeform, in the Red Earth Ecosystem Experimental Station, Academia Sinica. Results showed that soil microbial biomass could be sensible to indicate the effects of four types of vegetation on the bio-remediation of the degraded red earth ecosystem, to show the different effect of fertilization system on the fertility of red arable lands and to detect the pollution of Pacloutrazol and Chlordimeform applied to the red earth. Thus, the conclusion that soil microbial biomass may be as a bio-indicator of soil quality in the red earth ecosystem could be drawn.