In nourish period, lychee needs warm and wet weather, but in bud differentiation period, lychee needs moderate low temperature and drought. Based on the statistic analysis of the lychee yield and climate data in the last 50 years of 20 century, the key stage and temperature index in the lychee bud differentiation is determined. The key stage in the central part of Guangdong province for middle and latter maturity varieties is from the 2nd dekad of December to the 2nd dekad of January (about in the stage of anthotaxy anlage differentiation). The average temperature in four dekads of the key period is from 11 to 14℃, favor to bud differentiation, the rate of high yield year is about 70%. In a year with the average temperature from 15 to 17℃ for the key period is not favor to bud differentiation, the rate of lean year is about 75%. If in the partial warm year, before the 2nd dekad of January appears the moderate low temperature process, the average temperature in 2 dekads is lower than 15℃, so lychee can also have a better harvest.