Abstract: The field experiments show that supplementary irrigation can enhance the difference between the temperatures of leaf and atmosphere．The average photosynthesis rate of intercroppcd wheat and corn can be improved by 2．77％ and 24．85％ respectively than that of single planting in the whole growth stage．and it is positively correlated to the yield．Supplementary irrigation in critical stages can enhance the relative humidity in the canopy，and improve the photosynthesis rate and yield.