The invention discloses a same-floor drainage precision block prefabricated toilet with a reserved pipeline slotted hole in an inner wall, comprising four wall plates and a bottom plate which are prefabricated in a block manner, and the wall plates and the bottom plate are formed through splicing. A pipeline slotted hole, a door hole and window holes are reserved in the inner wall of the wall plates. A sinking layer is reserved at the bottom plate, a sewage collection pipeline is installed in the sinking layer, and the sewage collection pipeline is connected with a main drainage pipe. The sinking layer is filled with ceramsite and coated with cement mortar, and a cement mortar trowelled ground is formed. A pipeline well is arranged on the outer side of the main drainage pipe, ceramic tilesare pasted on the inner walls of the wall plates, the cement mortar trowelled ground and the pipeline well, and a bathroom sanitary appliance is installed at a set position in a bathroom. The prefabricated toilet is transported to a construction site, and is assembled on site by adopting hoisting. The surfaces of the partitioned prefabricated wall plates and bottom plate are flat, and required formworks are small. Drainage noise of a same-floor drainage system cannot affect lower-floor residents, and the pipeline groove hole reserved in the inner wall enable decoration to be quite attractive.