In order to use existing conditions with requiring no additional cost to improve the seismic capacity of tunnel in soft soil, the impact of grout on seismic performance of tunnel is studied and analyzed in the current paper. The compression modulus of grout could vary to the proportion of materials. The test results show which materials benefit for the compression modulus enhancing. And the results show relative displacement between top and bottom of tunnel, which is an important seismic performance index, decreases with the Es of grout increasing in certain range. Though the Es of grout should be larger than the Es of soil around the tunnel, it is unnecessary to pursue the over high Es of grout. It is necessary to take it into consideration for grout selection so that the tunnel could have better seismic capacity.