Abstract: The backfill grouting is the key technology in shield construction, which has good effect in controlling stratum deformation and segment up-floating. The suitability between the backfill grouting and the stratum is the core factor affecting its effect. Based on the investigation on backfill grouting materials of 144 shield tunnel projects in China, the specific value of grout ratio in round gravel stratum is obtained by the TOPSIS evaluation method and the injection tests. The research results show that the main type of grout is the single-component grout. Two-component grout or modified single-component grout are mostly used in the strata with groundwater. Confirmed by the injection tests, the range value of the grout ratio proposed by TOPSIS evaluation method is reliable. Through the injection tests, the specific value of the grout ratio is obtained. The optimum grout ratios in the round gravel stratum are 0.9 (water-binder ratio), 0.7 (binder-sand ratio), 0.2 or 0.3 (bentonite-water ratio), 0.4 (cement-fly ash ratio). The proposed optimization method may provide reference for selecting the speific grout ratios for different strata.