Visual inspection and hammering tests are the standard methods for inspecting shield tunnels. They can provide a comprehensive judgment based on the engineer’s past experience and conditions, such as cracking, water leakage, and structural details. However, one problem with this method is that the inspection results are highly dependent on the skills of the inspector. To overcome this limitation, it is necessary to develop an easy and quantitative inspection method for shield tunnels. The influence line (IL), which is the response at a specific point due to a unit load that is moved along the target structure, can be used for evaluating the soundness of the infrastructure. Therefore, in this study, we propose a method for determining the IL that can be applied when the speed of a passing train changes. The IL is determined by measuring the displacement due to the train load using a MEMS accelerometer. Finally, to verify the validity of the determined IL, a finite element analysis is performed. Good agreement is found between the ILs determined experimentally and analytically when the soil spring constant is 18 times higher than the nominal value, with a correlation coefficient of 0.98.