Abstract: The influences of several pretreatment conditions to nitrate nitrogen of contents of the composting process tested by UV-spectrophotometry are analyzed are compared with phenoldisulfonic acid colorimetry. The result showed that there is no difference between the nitrate nitrogen testing value of the phenoldisulfonic acid colorimetry and that of the UV-spectrophotometry, which the sample is extracted by KCl solutions and ultrasonic wave, and is treated by activated carbon. Also the influence of organic substance is removed and the operation is simple and convenient. The recovery of the modified method is 96%～108% and the coefficient of variation is 1.7%～5.5%.