Abstract: To study the effect of nitrogen form on photosynthetic characteristics, nitrogen metabolism related enzymes activity, accumulation of total alkaloid and free total organic acids of Pinellia ternata. A sand culture experiment was conducted and the content of chlorophyll, photosynthesis parameters, nitrate reductase（NR） activity, the content of nitrate in the leaves as well as the accumulation of total alkaloid and free total organic acids in the tuber were determined. Results: The content of photosynthetic pigment in the leaves of Pinellia ternata increased with the NH4+-N/NO3--N ratio increasing initially, then decreased. The contents of chlorophyll-a and carotenoid were the highest at the NH4+-N/NO3--N ratio of 75∶25；The content of chlorophyll-b, net photosynthetic rate, stomatic conductance and transpiration rate were the highest at the NH4+-N/NO3--N ratio of 25∶75. The activity of nitrate reductase decreased with the increase NO3--N ratio. The accumulation of total alkaloid in the tuber was the highest with the NH4+-N/NO3--N ratio of 0∶100, and declined with the decrease of NO3--N ratio. The content of free total organic acids increased with the enhancement of NH4+-N ratio. Conclusion: Proper ratio nitrogen fertilization is propitious to the growth of Pinellia ternata. A higher proportion of NO3--N is beneficial to the accumulation of total alkaloid; while a higher proportion of NH4+-N is beneficial to the accumulation of total free organic acids.