Based on the NCEP/NCAR, NCEP/DOE and ERA40 reanalysis data and the monthly precipitation data from 596 stations of China, the variation of the Tibetan Plateau (TP) summer monsoon and its impact on precipitation in eastern China are investigated by using the correlation analysis, the wavelet analysis, and the cross-spectral analysis. The results show that the plateau summer monsoon exhibits the strong interannual and long-term variability. It also shows an obviously upward trend during 1958-2010. The further analysis reveals that the abnormal enhancement of the plateau summer monsoon changes the Asia atmospheric circulation and then weakens the Asian summer monsoon. This leads to an increase of monsoon rainfall over the middle-lower reaches of the Yangtze River and a decrease over North China and South China. The strengthening of the plateau summer monsoon over the past 50 years may be related to the enhancement of thermal difference between the TP and its surrounding plains in the middle-upper troposphere (especially of the increase of thermal difference between the TP and the plain in eastern China).