The photosynthetic rate and the transportation of the photosynthate in high-density-tolerance corn were studied by useing14C tracing technigue. The results indicated that, the photosynthetic rate of corn hasn’t more difference between corn types. The photosynthesis was higher at 8—14 hours, and the photosynthetic rate 50—70mgCO2/dm2·h. The phosynthesis of corn has a noon-nap. The specific gravity of leaf was incrased within 12—14 hours in relation to the photosynthetic rate. Eighty pecent of photosynthate of leaf at ear position was transportad to other tissue and organ. The amount absorbed by ear was 50%—60%. The yield of Yiedan 13 increased 18% over Danyu13, on the average. Because the condensed planting increased the number of ears per unit area, the high density tolerant corn had higher yield.