In order to determine the temporal and spatial distribution characteristics of dissolved nitrogen and phosphorus in the LongtanReservoir during dry season, this paper made analysis of the main physical and chemical parameters by using stratified sampling slit in February2017 (dry season) and determined the dissolved nitrogen and phosphorus in laboratory. The results show that the water temperature has an obviousseasonal stratification variation： 0-10m is thermocline, 10-60m is mixed layer, and below 60 m is ethereal layer. The whole water environment isweakly alkaline because the values of pH are 7.63-7.92. The concentration of dissolved inorganic nitrogen (DIN) is 4.75mg/L. The ammonia(NH4+-N), nitrate(NO3--N) and nitrite(NO2--N) are 0.07mg/L, 2.62mg/L and 2.05mg/L accounting to 1.6%, 55.2%and 43.2%respectively of DIN.The nitrate (NO3--N) and nitrite (NO2--N) are the main parameters in DIN. The mean of phosphate concentration is 0.04mg/L. The LongtanReservior is eutrophication reference to the potential eutrophication evaluation standard with N/P values of 73.84. The spatial distributioncharacteristics of eutrophication is water body in front of dam> Shuangjiangkou> Hongshuihe Town> Xiaomachang .