Swelling rock is a type of soft rock ， which expanses and softens when wetted, but shrinks and disintegrates when dried. It has a better integrity in the early rock excavation in general, but if not protected in time, because of its significant expansion and contraction character, when the wet and dry cyclically occur, the characters often have tremendous changes, and seriously affect the security and stability of structures. In combination with practical engineering, the rapid protective material which is used in the excavated swelling rock drainage slope is studied through the test in this paper. The test results show that the rapid protective material, i.e. sprayed cement mortar(KS3) proposed by this paper, has good protecting effect on the weak swelling rocks, and that material KS3 not only can satisfy the rapid demand and be obtained from local discarded soil after excavation, also save the quantity of cement, bring notably economic benefit. So it is worth recommending.