Abstract: In order to explore the effects of plant growth regulators on the seed yield of alfalfa, a random block method was used in this experiment. Longmu 801 was selected as the research object, and two plant growth regulators, Mepiquat chloride（80,160,240 mg/L） and Bijiu（3 000,5 000,7 000 mg/L） were sprayed to alfalfa seed fields at the budding stage and the full flowering stage, respectively. The effects of different treatments on the yield and constituent factors of alfalfa seeds were examined at the maturity stage, and correlation analysis and stepwise regression analysis were carried out. The results showed that the seed yield treated with Mepiquat chloride and Bijiu（except for 7 000 mg/L） was significantly higher than that in the control（P＜0.05）. Each yield component factors were positively correlated with seed yield, and the number of reproductive branches per square meter in the spraying Mepiquat chloride groups was significantly positively correlated with seed yield（P＜0.05）. There was a significant positive correlation between the number of pod inflorescences/reproductive branch and the seed yield（P＜0.01） in the spraying Bijiu treatment, and a significant positive correlation between seed/pod number and seed yield（P＜0.05）. The stepwise regression equation between seed yield and yield component factors in the sprayed Mepiquat chloride treatment was Y=2.043 9+0.216 5X₁（Y was seed yield, X₁ was the number of reproductive branches per square meter）. The stepwise regression equation between seed yield and yield component factors in the spraying Bijiu treatment was Y=17.175 3+0.049 1X₁+0.932 7X₂+3.874 8X₄（Y was the seed yield, X₁ was the number of reproductive branches per square meter, and X₂ was the number of pods/reproductive branches, X₄ was the number of seeds per pod）. The results indicated that the spraying of Mepiquat chloride and Bijiu could significantly increase the yield of alfalfa seeds.