By using 1958—1998 NCEP/NCAR reanalysis,1975—1998 OLR and 1973—1998 monthly snow cover days(SCD) at 115 stations over the Tibetan Plateau(TP) and its peripheral areas,the possible mechanism of impacts of winter-spring snow cover on the South China Sea(SCS) monsoon onset is investigated.The increase in winter-spring snow cover is associated with the weakening of sensible heating over the TP,and with the decrease in temperature in the middle-upper troposphere over the TP and its east side,thus leading to a later reversion of large-scale meridional temperature gradient.At the same time,the seasonal reversion of Hadley Circulation in the TP region will also take place later than normal,with the abmormal descent airflow maintaining over the Indo-China Peninsula(ICP),causing a later split of the subtropical high over the Bay of Bengal,and a later outbreak of convective activities over the ICP,in such a way that the surface temperature over the ICP will decrease later,resulting in a later reversion in local zonal temperature gradient between the ICP and the SCS.The SCS monsoon may outbreak later under the joint action of the above large-scale meridional and local zonal temperature gradients.