As passing through the hilly areas and the midlow mountain areas of Hunan province and the high mountains on the eastern margin of YunnanGuizhou Plateau, a large number of bridges and tunnels are necessary in Hunan section of ChangshaKunming Passenger Dedicated Line, which increases design difficulties and construction risks. In order to solve the problems of design and construction caused by bridgestunnels connection in complex mountainous regions, many high and steep portals with unsymmetrical load, and poor geological conditions such as rock piles or bedding in some tunnel portals, the bridgestunnels connection projects in complex mountainous regions are divided into three connecting types, i.e. overlapping bridges structure and linings of tunnel portal, separating abutment and tunnel portal structure, closing abutment and tunnel portal structure (with short subgrade), based on the characteristics of high speed railway tunnel and the relationship of bridgestunnels connection projects under complex conditions. In addition, the method of connecting tunnel and bridge by overlapping bridges structure and linings of tunnel portal with separating beating structure is developed and applied in highspeed railways to solve the design difficulties of connecting bridge and tunnel portal in bridgestunnels connection projects. By studying the topography and geology conditions of high and steep portals with unsymmetrical load, some schemes, i.e. "ear wall + arch protection + back pressure backfilling" technology for underground excavation, frontal protection technology for anchor piles, and supporting technology for base piles and pallets, are proposed for tunnel portal construction to solve problems of difficulty in entering the hole, bad geology of the portal, hard and soft stratum or partial suspension of tunnel bottom, and construction risks, etc.