The invention discloses a casing pipe for repairing loess roadbed and a method for repairing loess roadbed, which solves the technical problem that pipes injected with water into the roadbed can be blocked in the prior art. The sleeve for repairing the loess roadbed comprises an outer sleeve whose bottom end closes the top end opening, A wat injection pipe is arranged in that out pipe, The water injection pipe comprises a water injection hole section, a plurality of water injection holes are arranged on the pipe wall of the water injection hole section, The water injection hole section is coated with a gauze net, and an anti-detachment structure is arranged between the outer sleeve and the water injection pipe. When the casing sinks along the drilled hole, the water injection hole sectionis protected by the outer sleeve, so as to avoid the water injection hole on the water injection hole section being blocked by soil during the sinking process. When water is injected, the gauze net can protect the water injection hole section and prevent the mud in the hole from blocking the water injection hole. The method for repairing loess roadbed of the invention calculates the amount of water to be injected into the roadbed according to the position and height of the roadbed to be subsided, and the arrangement distance and the range of the sleeves, so that the subsidence height of the loess roadbed can be actively controlled.