Abstract: The relation between the number of the May heavy storm days in Yunnan and the Asia monsoon intensity index is studied by correlation analysis and EOF methods.It is indicated by the results that there is a good correlation between the May heavy rainfall and the South Asia monsoon index.The correlation coefficients of the corresponding period,May,and the previous period,April,are 0.493 and 0.447 respectively,and go beyond 99% significance level.The correlation coefficient of the previous period,January,is 0.312,and goes beyond 95% significance level.The good correlation between the May very heavy rainfall and the the South Sea monsoon index is in the previous period,April,when the correlation coefficient is 0.415 and goes beyond 98% significance level,but the correlations of other months are not significant.The 11 yeas’ running correlation coefficients also indicate that the effect of the South Asia monsoon on the May heavy rainfall in Yunnan is bigger than that of the South Sea monsoon.Three spatial distributions of the May heavy-storm days in Yunnan are obtained by EOF method.There is a good correlation between the first spatial distribution and the Asia monsoon index,especially the South Asia monsoon.There is also a good correlation between the second spatial distribution and the South Sea monsoon index.The effect of the Asia monsoon on the third spatial distribution is not obvious.