There is obvious Quasi-Biennial variability both in summer precipitation over South China(SCSPR) and Summer Monsoon over South China Sea(SCSSM).After the 1970s interdecadal variations of SCSPR mainly behaved as the interdecadal variation of the averaged variance of quasi-biennial oscillations,and generally the larger variance corresponds to the more summer precipitation in South China,and vice versa.But there was no such a relation before 1976.The analysis results suggest that it is due to the interdecadal change of the quasi-biennial relationship between SCSPR and SCSSM.In the interdecadal phase of 1953—1976,the SCSPR and SCSSM exhibited a weak negative correlation of the quasi-biennial timescale components,while there was a strong positive correlation between their non-biennial timescale components;and during 1977—2000,the TBO(Tropospheric Quasi-Biennial Oscillation) of SCSPR and SCSSM varied in phase,there was no meaningful relation between their non-biennial timescale components.Further analysis indicates that the catastrophe of atmospheric general circulation in 1970s made the quasi-biennial variation of SCSPR dominate over the interannual variations in the recent more than 20 years.