Based on the NCEP / NCAR wind field, specific humidity, surface pressure and precipitation reanalysis data from 1951 to 2010, a cross equatorial moisture transport intensity index is established to characterize the strength of the Somali jet (SMJ), and the seasonal, interannual, decadal variations and mutations of the SMJ cross equatorial moisture transport intensity are studied, while comparing with the traditional SMJ wind speed intensity index. In addition, the relationship between SMJ and the China early summer precipitation is analyzed. Based on the above analysis, the decadal changes of this relationship are revealed. Main results are as follows. After the 1990s, the SMJ wind speed intensity index is weakening, but the SMJ water vapor transport has no significant variations; compared with the SMJ wind speed strength, the SMJ water vapor transmission intensity is associated with the China early summer rainfall more closely. When the SMJ is weaker, rainfall decreased in the Huanghe Huaihe River Basin and North China in early summer, and vice versa. Besides, this correlation has been strengthened in recent 30 years.