Potassium chlorate was applied to ‘Shixia’ longan trees as soil drench in the period of flower bud differentiation, some biological indexes were researched. The conclusion was: 1 The contents of CHL was induced. 2.Net photosynthetic rate was reduced in period of physiological differentiation, and was raised in period of morphological differentiation. 3.Contents of soluble sugar, reductive sugar, and soluble protein were increased in evidence. 4. Contents of endogenetic ethylene (ETH) outclassesed CK, the speed of ETH peak coming depends potassium chlorate dosage, the bigger dosage the sooner speed. 5. Activity of POD enzyme was under then CK, but higher than traditional promoting flower measures for example spraying ETH. 6. The rate of flower shoot was a little higher then CK, the rate of panicles with aborted fruits was significantly lower, and the yield per tree was significantly higher then CK.