The invention discloses an improved rotary fine screen for filtration of water treatment. The rotary fine screen is characterized in that: a rotary annular filter screen is formed by hinging triangular hopper-shaped porous filter plates, wherein each triangular hopper-shaped porous filter plate has an open edge, and is annularly arranged on a frame in a way that triangular openings are inward; a slag collection and discharge device comprises a slag collection hopper and a lower conveying and slag discharge device, and is arranged in the rotary annular filter screen; and a thickness surface on one side of the screen is closed and a thickness surface on the other side of the screen is open. The filtering area of a single filtering surface at least can be increased by 10 to 20 percent compared with that of a single filtering surface of a planar filter screen; and moreover, two surfaces of the rotary screen have a filtration interception effect, and the filtering area is at least increased by 120 to 140 percent. The filtration mode that sewage flows from inside to outside also ensures that intercepted dirt and filtration effluent are completely separated, so that the intercepted dirt cannot be brought into the downstream of the effluent along with the rotation of the filtering surfaces of the screen. Particularly, the open thickness surface is arranged toward the water flow, so that the filtration flux is not affected by the width of a canal, the rotary fine screen can still be put into the original canal after the width is increased, the dependence on the width of the canal is greatly reduced, and the floor area of the canal is saved; and the rotary fine screen is particularly applicable to the transformation of old sewage treatment plants.