Fifteen sites were selected for water sampling from the Xiaohe River watershed to study the distribution of ammonia

nitrate and nitrite and their relationship with dissolved oxygen. It was found that the contents of HNO2-N at all the sampling sites are relatively high. Except water conservation area with a gradeⅠ of surface water quality according to the national standard(GB3838-2002)

the rest sites belonged to Grade Ⅳ

which was associated with the discharges of both industrial and domestic effluents along the river system of Xiaohe River in Jinzhong section and Baima River in Shouyang section. The contents of water nitrogen have a reamarkable change in river interchange and channel slope mutation place. Three nitrogen were affected by the contents of water dissolved oxygen in different degree:the contents of NH3-N and HNO2-N at all the sampling sites reduced with the increase of dissolved oxygen. Influenced by NH3-N

the contents of HNO3-N at S3

S4

S7

S9 and S12 Sites were reduced with the increase of dissolved oxygen

the contents of HNO3-N at all the rest sites increased with the increase of dissolved oxygen. The linear regression analysis showed that only the contents of HNO2-N had a significant correlation with dissolved oxygen.