Abstract: It was studied that different ecological conditions affected on the flower bud differentiation and fruit setting of sweet cherry to identify the critical period that influences sweet cherry fruit setting in warm regions. First，we transported some potted sweet cherry trees（Prunus avium L.）from Zhengzhou to Nanjing to make them grow for a year，then took the potted trees growing in Zhengzhou and Nanjing as test materials. The treatment included the exchange of trees between Zhengzhou and Nanjing at the stage of leaf fall in winter and before budding in spring. The bud paraffin sections were made to observe the difference on the development of flower bud and embryo sac. The fruit setting rate was investigated at the stage of fruit coloring. The results were as follows：The fruit setting rate of the cultivar‘РубиноваяРанняя’growing in Zhengzhou for whole season，transported from Zhengzhou to Nanjing at the stage of leaf fall，transported from Zhengzhou to Nanjing before budding，growing in Nanjing for whole season，transported from Nanjing to Zhengzhou at the stage of leaf fall was 38.2%，14.7%，12.9%，8.9% and 31.7%；The percentage of the bud that had ovule but no embryo sac was 41.5%，55.6%，57.7%，74.5% and 50.0%，respectively. Fruit setting rate of‘Summit’were that totally growing in Zhengzhou and that transported from Zhengzhou to Nanjing at the stage of leaf fall then transported to Zhengzhou when the dormancy period finished was 13.9% and 18.8%，respectively. These indicated that the blooming and setting stage may be the critical period that leads to low setting rate in warm areas. For some cultivars of low chilling requirement，dormancy period has virtually no effect on fruit setting. The high temperature in summer has little influence on fruit setting during the period of flower bud differentiation but obviously affects the bud development status and quality.

Key words: sweet cherry, setting rate, bud development, critical period