Abstract: 【Objectives】 Chemicals have played important roles to improve crop yields, proper application will be effective in regulating the physiological metabolism of crops. The study on the effects of plant growth regulators on the leaf physiological activities of soybean will provide scientific basis for their efficient use in soybean production.【Methods】 Foliar spray field experiments were conducted successively in 2013 and 2014 in the main soybean producing zone, Heilongjiang Bayi Agricultural University. Experiment was in the early flowering by foliar spray one time. Two chemical regulators, 2-N, N-diethylamino ethyl caproate (DTA-6, 60 mg/L) and uniconazole (S3307, 50 mg/L) were tested with water as control. The first sampling was carried outafter sprayed 30 d, and then leaf samples were collected once every five days. The contents of soluble sugar, sucrose, starch and total amylase activity were measured. The grain yields of soybean were investigated.【Results】Foliar spray of S3307 and DTA-6 could significantly increase the chlorophyll content of leaves, especially the lower located ones. In the 22nd day after spray, the chlorophyll content in the 3rd leaves from the top was increased by 9.32% and 7.02% by foliar spray of S3307 and DTA-6, respectively, and those in the 9th leaves from the top by 11.12% and 10.38% respectively. The chlorophyll contents in the third and the ninth leaves from top were significant and positively correlated with yield. The soluble sugar contents in the two leaf samples were always higher than those in control after 40, 45 and 50 days of spraying, The sucrose contents reached the maximum at the 40-50 days and 35-50 days since spraying of DTA-6 and S3307, and more sucrose was accumulated in plants sprayed with S3307 than with DTA-6. Starch contents were all higher than the control after the 50th, 55th and 60th day since the spraying by DTA-6 and S3307. At the 45th day of spraying, the amylase activity in control decreased to minimum, but those in treatments reached maximum, and the amylase activity sprayed with S3307 was higher than with DTA-6. Two regulators increased the number of pods, grains per plant, grain weight per plant and yield. The increase in pods number and grains per plant in treatment S3307 reached a significant level, compared with control, those in treatment DTA-6 did not reach significant levels. The yield of both S3307 and DTA-6 treatments were significantly increased by 20.00% and 15.00% in average in the two years experiments.【Conclusions】Foliar spray of S3307 and DTA-6 could significantly enhance physiological metabolism in the early flowering. Especially, at the 50th day of spraying, when was just in the grain filling stage. The content of soluble sugar, sucrose and starch was significantly higher in the two treatments than those in control. Plant growth regulators could significantly enhance physiological activities and delay the senescence of soybean leaves during middle-late growth stages. Thereby, it was effective to increase seed yield.