An open type fine-tuning sight, comprising a housing mainly provided with a straight portion and a lens mounting frame provided at a front end of the straight portion, characterized in that, the housing comprises an outer housing assembly and an inner housing assembly sleeved in the outer housing assembly; the inner housing assembly is sleeved in an installation space at a front end of the outer housing assembly, and a front end of the inner housing assembly is connected to the front end of the outer housing assembly through a parallel connecting rod assembly comprising two connecting rod groups that passes through transversely; the inner housing assembly comprises a base and an arc-shaped lens mounting frame of which both ends spanned at the left and right sides of a front end of the base; the arc-shaped lens mounting frame is arranged in the lens mounting frame and is in clearance fit with the lens mounting frame; the front end of the base is provided with two arc-shaped convex surfaces with arc-shaped end surfaces below inner connecting rod perforations through which the connecting rod groups of the connecting rod assembly passes, the two arc-shaped convex surfaces are respectively disposed on left and right sides of an axial direction of the base; the inner sides of left and right ends of a bottom surface of the front end of the straight portion corresponding to the two arc-shaped convex surfaces are each provided with an arc-shaped concave surface to match with the arc-shaped convex surfaces; the left and right sides of the bottom surface of the front end of the straight portion are provided with outer connecting rod perforations corresponding to the inner connecting rod perforations and coaxial with the inner connecting rod perforations above the arc-shaped concave surface; an end portion of the front end of the base is an arc-shaped protruding surface protruding outward, and the arc-shaped protruding surface is arranged in an arc-shaped inner concave surface of the bottom surface of the front end of the straight portion; an elastic piece is provided between one side of a rear end of the base and one side of a rear end of the straight portion, the elastic piece is used to cooperate with a fine-tuning mechanism that passes through the other side of the rear end of the straight portion from an outside to an inside and is installed in the rear end of the base to adjust a lateral angle of the inner housing assembly; a vertical return spring sleeved on a connecting screw is provided between the rear end of the base and the bottom surface of the straight portion to cooperate with the fine-tuning mechanism to adjust a pitch angle of the inner housing assembly; the connecting screw is threadedly connected with a bottom surface of the base after being penetrated upward from the bottom surface of the straight portion. the inner housing assembly is sleeved in an installation space at a front end of the outer housing assembly, and a front end of the inner housing assembly is connected to the front end of the outer housing assembly through a parallel connecting rod assembly comprising two connecting rod groups that passes through transversely; the inner housing assembly comprises a base and an arc-shaped lens mounting frame of which both ends spanned at the left and right sides of a front end of the base; the arc-shaped lens mounting frame is arranged in the lens mounting frame and is in clearance fit with the lens mounting frame; the front end of the base is provided with two arc-shaped convex surfaces with arc-shaped end surfaces below inner connecting rod perforations through which the connecting rod groups of the connecting rod assembly passes, the two arc-shaped convex surfaces are respectively disposed on left and right sides of an axial direction of the base; the inner sides of left and right ends of a bottom surface of the front end of the straight portion corresponding to the two arc-shaped convex surfaces are each provided with an arc-shaped concave surface to match with the arc-shaped convex surfaces; the left and right sides of the bottom surface of the front end of the straight portion are provided with outer connecting rod perforations corresponding to the inner connecting rod perforations and coaxial with the inner connecting rod perforations above the arc-shaped concave surface; an end portion of the front end of the base is an arc-shaped protruding surface protruding outward, and the arc-shaped protruding surface is arranged in an arc-shaped inner concave surface of the bottom surface of the front end of the straight portion; an elastic piece is provided between one side of a rear end of the base and one side of a rear end of the straight portion, the elastic piece is used to cooperate with a fine-tuning mechanism that passes through the other side of the rear end of the straight portion from an outside to an inside and is installed in the rear end of the base to adjust a lateral angle of the inner housing assembly; a vertical return spring sleeved on a connecting screw is provided between the rear end of the base and the bottom surface of the straight portion to cooperate with the fine-tuning mechanism to adjust a pitch angle of the inner housing assembly; the connecting screw is threadedly connected with a bottom surface of the base after being penetrated upward from the bottom surface of the straight portion.