Abstract: The effects of nitrogen forms, rates and plant population on photosynthesis and nitrate reductase (NR) activities of oriental tobacco were investigated in Baoshan oriental tobacco growing areas of Yunnan Province.The results showed that applying nitrogen with a blend of NO₃^--N and NH₄⁺-N while comparing with applying NH₄⁺-N only, was more conducive to raising the content of chlorophyll, NR activities and photosynthesis rate.The preferable ratio of NO₃^--N to NH₄⁺-N was 1-2 to 1.With the same plant population, the content of chlorophyll and NR activities were increased by increasing nitrogen rates.With the same nitrogen rates, no rule was found in the change of chlorophyll content, while NR activities were decreased by increasing plant population.The treatment of medium nitrogen application rates and plant population (A2B2)obtained the highest photosynthesis rate.