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.