Abstract: This paper studied photosynthetic rate of wheat intercropped with 7 year-old poplars by isotopic tracer technique. The difference of net photosynthetic rate between intercropped wheat and field wheats steadily increases along with the increase of canopy density of poplars. In the seedling stage of wheats fed to leaves with 14CO2 for 30 minutes, 14C can be kept in tissues for 7 weeks at least, and the 14C content of intercropped wheats is higher than that of field wheats.