Abstract: In this paper, deep connective characteristics of summer monsoon onset over Asian region are investigated. Data sets used are the US Climate Prediction Center (CPC) Merged Analysis of precipitation (CMAP),US National Meteorological Center (NMC) globe wind analysis, Outgoing Longwave Radiation (OLR) and upper-tropospheric water vapor band brightness temperature (BT) observed from NOAA polar orbiting satellites for 1980-1995. The BT, OLR and wind at 850 hPa are first compared to the CMAP. Results show that the BT can indicate the convective precipitation in both tropical and mid-latitude regions but the OLR can not well reflect the precipitation in the region of mid-latitudes. The convergence of wind field can explain the burst of summer monsoon and its extension. The region of Asian summer monsoon is the largest one of deep convection seasonal variation over the world. Also, in this paper, the summer monsoon over the mid-low latitudes was defined as the seasonal expansion of deep convection coming from tropical region with the criterion of BT less than 244 K. The summer monsoon over the Indo-China Peninsula bursts before the onset of the South China Sea (SCS) summer monsoon. The deep convection over South China during the pre-rainy season results from the interaction between middle and lower latitude systems. In the 28-th pentad, the abrupt onset of the SCS summer monsoon can be directly identified through the monitoring of OLR, BT, CMAP and 850 hPa wind. After the onset of the SCS summer monsoon, the summer monsoon of Indian subcontinent gradually sets up from south to north, while the northward extensions of summer monsoons over the east Tibetan Plateau and the East China Sea are earlier than over central China.