Abstract: Using Kjeldahl method to determinate the total N in solutions needs to concentrate and reduce the NO3--N and NO2--N to NH4+-N. That is unconvenient.Recently,because of its convenience and rapid, the alkaline persulfate oxidation method(APOM)proposed by Koroleff was used to determine the total N in seawater and soil extracts. It is found that there is a close relationship between the oxidation efficiency and the composition of oxidizer, however, the composition of oxidazer used by researchers was various. Therefore, the object of this research was to choose a proper oxidzer for APOM.The concentraction of the oxidizer using to determine the total nitrogen in solution by alkaline persulfate oxidation showed that there was a close relationship between the pH of solution in oxidation reaction and the efficiency of oxidation.The concentration of persulfate and NaOH of the oxidizer was key for converting other form nitrogen into NO3--N. It was concluded that 3% persulfate combined with 0. 15 molL-1 NaOH was a suitable oxidizer: its maximum limit of detecting urea-N was about 80mg. L-1; and could recover the nitrogen of L-alanine and EDTA in solution quantitatively. Total nitrogen determined by alkaline persulfate was agreed with that by Kjeldahl method.