Abstract: The canopy microclimate of two new maize hybrids was studied under high yield condition in 1997-1998, farm-based field experiment in Jinan. Photosynthetic photon flux density (PPFD), CO2 concentration, air temperature, and wind velocity were significantly affected by plant density. The role of microclimate in affecting levels of available stored energy in grain was confirmed, and it is suggested that higher available stored energy could be obtained in grain by adjusting plant density and thereby adjusting microclimate.