The Eurasian blocking circulation anomalies over the mid-high latitudes during summer is one of the primary circulations associated with southern China droughts and floods. And the formulation of blocking circulation is closely related to atmospheric internal modes and external forcing factors which are playing an increasingly important role. In order to investigate the cause of blocking circulation anomalies on the interannual and decadal timescale, it is crucial to explore the impact of preceding external forcing factors and the mechanisms responsible for the influence. However, previous studies focus mainly on single external forcing factor as well as its influence, and far little attention has been paid to the combined impact of multiple factors. Therefore, in the present study, on the basis of critical processes in sea-land-air interaction, we attempt to identify the key external forcing factors, such as Arctic sea ice, Eurasian snow cover and North Atlantic sea surface temperature, and further to analyse the decadal changes in the relationship between key factors and circulation anomalies over the blocking domains. In view of the configuration of key factors, the physical mechanism responsible for the combined impact of key factors on the circulation anomalies over the blocking domains will be diagnosed by investigating the heating and transient vorticity forcing, via observational data and numerical simulation. Furthermore, the experienced forecast models would also be constructed. In the present project, we are beginning to get a deeper insights into the combined impact of preceding external forcing factors on the summer circulation anomalies over the Eurasian blocking domains. It aims to provide a scientific basis for improving the skill of summer climate forecast and thus increasing the ability to deal with disasters.