Comprehensive investigation is made of the longitudinal and latitudinal variations in the large-scale circulation from May to June in terms of spherical expansion.It is found that the spectrum features of the mean large-scale circulation are different at various levels and a spherical wave can be found as the sample for the longitudinal wave at each level. The variations in the features of spherical wave spectrum reflect the at mospheric circulation catastrophe in June, which develops from the 100hPa to 500hPa level, and is most significant at the 500hPa level. The characteristics of spherical spectrum are different in wet and dry years and there exists a pronounced difference between the phase of the predominant wave before the beginning of the Mei-yu season and the conversion wave after the period.