The invention belongs to the technical field of tunnel construction machines, and mainly relates to a narrow loader multifunctional side-dumping bucket suitable for a single track railway tunnel. The narrow loader multifunctional side-dumping bucket suitable for the single track railway tunnel comprises a bucket bottom plate, a bucket top plate, a gate I and a gate II, wherein the gate I and the gate II serve as side wall plates of the bucket; the bucket bottom plate and the bucket top plate form a bucket-shaped structure with the left end, the right end and the front end opened, the gate I and the gate II are arranged at the left end and the right end of the bucket-shaped structure, and a gate rail I and a gate rail II used for the gate I and the gate II to vertically slide respectively are arranged at the left side and the right side of the rear end of the bucket-shaped structure; a rack is fixed to the top of the outer wall face of the bucket top plate, and an arc rail is arranged on the rack; a pin shaft capable of horizontally sliding in the arc rail is correspondingly arranged on the arc rail. The requirement for dreg discharging of the single track railway tunnel and movement of the operation rack is met, multipurpose function and automatic construction are achieved, construction cost is saved, and the construction period requirement is ensured.