Abstract: In order to simplify measurement of soil microbial biomass nitrogen(SMB-N), a study on comparison of total nitrogen (Ntot) in soil extraction and SMB?N estimated by continuous flow analytical system (CFA) and Kjeldahl digestion methods was conducted based on determination of nitrogen partions existing normally in soil extraction The results showed that the recovery of standard organic nitrogen of various components reached to a mean value of 94%, and there existed significant correlation and similar tendency of content of Ntot and SMB-N measured by CFA and Kjeldahl methods The amount of SMB-N estimated by CFA method accounted for 78% or 84% of that estimated by the Kjeldahl method and these observations all come from the same fraction of the soil nitrogen The Kn value for determination of soil microbial biomass nitrogen by CFA method should corrected to Kn=0.48 (CaCl2 as extractant) or Kn=0.53(K2SO4 as extractant)