Discriminant analysis is an important method in multivariable statistic analysis to show what type an individual should belong to. Based on actual field photosynthetic value set obtained from our research platform, North East China Transect (NECT), a new approach, developed from the concept and principle of discriminant analysts, was proposed to distinguish C3 and C4 plants. Indices related to plant photosynthetic capacity measured by an LCA4 photosynthesis system were selected to build the discriminant model which is based on four related parameters: net photosynthetic rate, transpiration rate, stomatal conductance, and difference in temperature between leaf surface and atmosphere. Compared with other approaches, the present one is fast, straightforward, and efficient. and H. P. Tang, X. S. Zhang.