Abstract: When evaluating the mitigation effect of a vibration isolated track in an operating metro line, two test sections on the vibration isolated track and reference track are often selected, and then the contrast loss is calculated. However, the dynamic characteristics difference of the stratum behind a tunnel can affect the evaluation results. To quantitatively analyze the influence of this factor, a vehicle-track coupling model was established to calculate train loads. Using the finite element software, a track- tunnel-stratum three-dimensional numerical model was developed, considering two types of track-form. The difference between the contrast loss and the insertion loss caused by the three parameters (dynamic elastic modulus, Poisson's ratio and mass density) of the formation were analyzed and discussed. A quantitative correction method for contrast loss based on the difference of dynamic characteristics of strata is presented. The results show that: the difference of dynamic elastic modulus is the main parameter of the difference in dynamic characteristics of the stratum in the test section, which has a significant effect on the contrast loss of vibration isolated track; if the dynamic elastic modulus of the stratum at the test point is less than 500 MPa, the difference of stratum dynamic characteristics between the test sections will have a more significant influence on the evaluation results of damping effect.