Taking a shield tunneling project section in Xiaoshui as a case study， research was conducted to solve the key problem of the proportioning of grouting materials under karst geological conditions. A series of pre-tests were carried out in the pre-test period using raw materials such as clay， sand， gravel and cement， on the basis of which orthogonal tests on the factors of paste slurry proportioning were carried out by means of in situ soil extraction. The test results show that the dry clay and water-cement ratio are the factors that have the greatest influence on the compressive strength of the paste； The main influencing factor of the slump of the paste is the water-cement ratio， and the mixing amount of dry clay and sand contributes to the slump quite a lot； In terms of the compressive strength， the degree of contribution is in the order of the water-cement ratio>dry clay>sand. Considering the performance parameters and economy of paste slurry， it is recommended to choose No.6 （A2B1C3） paste slurry as the filling grouting material for this construction. The results of the study show that the preparation of paste slurry using clay and mechanism sand from the construction site can meet the requirements of the Design Institute for the performance index of karst filling materials.