To find the rational planting density of new variety Maize Songyu 419 insemi-humid zones of Jilin Prov-ince, field experiment was carried out. Five planting densities were designed, which were 50 000, 56 000, 63 000,72 000, and 83 000 plants / ha. Under the different planting densities, the population physiological characters, yieldand yield traits of Songyu 419 were researched. The result showed that the relativechlorophyll content and single drymatter weight decreased and population photosynthesis potential increased as planting densityincreased. Populationdry weight as well as the yield showed a curve of first increase and later drop. It is suggested that the high yield ofSongyu 419 had earned in planting density 63 000 plants /ha and the yield reaches 12 820.5 kg/ha.