Lying between China，South Asian sub-continent and Southeastern Asian Islands，the Greater Mekong Sub-region is called Indochina Peninsular or on-Land ASEAN. Connecting China with South Asia and Southeast Asia，this sub-region is adjacent to South China Sea，the Strait of Malacca，the Andaman Sea，and Bay of Bengal，which gives it important geographical position. Endowed with water resources and mineral resources，this sub-region boasts great economic potential and has for centuries been the arena for wrestling between major powers. The bilateral and multi-lateral cooperation mechanisms can not fully address the increasingly complicated and various security problems in this sub-region. In light of these developments，it is necessary to construct the security mechanism of the Greater Mekong Sub-region involving six countries.