The transbasin waterway of AKungTien Reservoir is apart of the rehabilitation project of AKungTien Reservoir. It plays very important role on supplying water resource in the Kaohsiung area of south Taiwan. The national highway No.3 is an important line of the traffic in south Taiwan. Because the tunnel needs to pass through the pierfooting of the national highway No.3, it is doubt that if the original design could cause the settlement of pierfooting or not. It was resolved to change the design and revise the alignment of the tunnel after discussion, and processes the geological survey along the modified tunnel. The geological parameters will be used to estimate the safety of the structure of the bridge by numerical simulation analysis. The analysis result is that settlement and angle variable are within the permitting range. With the proper construction way and complete monitoring system, it shows that the result is in conformity with value of the numerical simulation. It also shows that the safety of the bridge of the national highway No.3 can be ensured by effectively controlling the diplacement of the surroundings of tunnel in this case.