In the test, the population of Elymus sibiricus L. Was sprayed with different concentrations of paclobutrazol or chlormequat chloride in the jointing or booting stage. Some parameters of reproduction investment, such as fertile branch density and rate, inflorescence biomass density and rate, inflorescence energy density and rate, parameters of reproduction return, such as seed yield, maturation rate and return rate, parameters of seed quality, such as 1000-seed weight, germination index and seed vigor index, were analyzed by using multiple comparison. The results showed that: there was a highly significant effect of growth inhibitor on reproductive investment of population (P <0. 01). And the type, concentration, application time of inhibitor had an effect on density of fertile branch, density of inflorescence biomass and energy. Paclobutrazol significantly promoted accumulation of biomass and energy of population inflorescence, but chlormequat chloride inhibited transfering biomass and energy of population into inflorescence. And for reproductive investment of population, the application effect at the jointing stage was significantly stronger than that of booting stage. Growth inhibitor highly significantly affected potential seed yield, harvested seed yield, maturation rate and return rate(P <0. 01). And for seed production, the effect of paclobutrazol was stronger than that of chlormequat chloride. After applying paclobutrazol of 200~800mg/L at jointing stage, seed yield was significantly increased(P<0. 05). In particular, 600mg/L paclobutrazol increased potential seed yield and harvested seed yield by 46. 21% , 65. 89%, respectively, which was worth promoting in practice. But applying paclobutrazol would decrease maturation rate and return rate of seed. Growth inhibitors had highly significant effects on 1000-seed weight, germination index and vigor index (P <0. 01). At the jointing stage applying inhibitor would raise germination index of seed, while application at booting stage would reduce germination index. No obvious regular pattern was found among germination index and vigor index in different condition of type and concentration of retardant.%在拔节期、孕穗期分别施用不同浓度的多效唑或矮壮素,对老芒麦种群的生殖投入参数(生殖枝密度及比例、花序生物量密度及比例、花序能量密度及比例等)、生殖收益参数(种子产量、成熟率、收益率等)和种子质量参数(千粒重、发芽指数、活力指数等)进行了比较分析.结果表明:生长抑制剂对种群生殖投入有极显著影响(P＜0.01),抑制剂种类、浓度及施用时间对生殖枝密度、花序生物量与能量密度均有影响；多效唑显著促进种群花序生物量与能量累积,矮壮素则抑制种群生物量、能量向花序分配；拔节期施用比孕穗期施用更有利于种群的生殖投入.生长抑制剂对潜在种子产量、实际种子产量、成熟率及收益率均有极显著的影响(P＜0.01),其中多效唑对种子产量的促进作用显著高于矮壮素,拔节期施用200～800mg/L的多效唑可显著提高种子产量(P＜0.05),尤其是施用600mg/L的多效唑使潜在种子产量、实际种子产量分别比对照提高46.21％、65.89％,值得在生产中推广应用,但多效唑降低了种子成熟率与生殖投入收益率.生长抑制剂对种子千粒重、发芽指数与活力指数有极显著影响(P＜0.01),拔节期施用可提高种子的发芽指数,孕穗期施用则降低发芽指数；抑制剂种类、浓度对发芽指数与活力指数的影响无明显规律.
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