Abstract: In order to study the effect of different sowing dates on the main agronomic traits and yield, close planting soybean cultivar‘Hefeng51’, which was planted in the third temperate zone of Heilongjiang Province, was uesd as test material and five sowing date treatments (S1 was May 10th, S2 was May 20th, S3 was May 30th , S4 was June 9th, S5 was June 19th) were set to study the change rule of the main agronomic traits and yield under different sowing dates. The results showed that the plant height, the main stalk pitch number and the hundredgrain weight showed a gradually reducing trend. The number of pods and seeds per plant showed a decreasing trend after the increase. The soybean yield showed a decreasing trend after the increase. The highest yield of 4214.3 kg/hm2 was obtained by S3 treatment. So the best sowing date of‘HeFeng51’was May 30th in the east area of Heilongjiang Province.