The invention relates to annular slit restrictor comprising a restrictor mounting body and a restrictor body. The restrictor body is arranged in the restrictor mounting body; the restrictor mounting body comprises a step-shaped front end cavity and a step-shaped rear end cavity; the restrictor body comprises a step-shaped front end part, a step-shaped middle part and a step-shaped rear part, wherein the front end part is axially positioned by hole shoulder of the restrictor mounting body, and the middle part and the rear part are arranged in the rear end cavity of the restrictor mounting body; the middle part of the restrictor body is axially matched with the rear end cavity of the restrictor mounting body; the diameter of the rear part of the restrictor body is smaller that that of the rear end cavity of the restrictor mounting body; the slit between the rear part of the restrictor body and the rear end cavity of the restrictor mounting body forms the working zone of the annular slit restrictor; and the front end part and the middle part of the restrictor body are provided with through holes which are communicated with the working zone. The annular slit restrictor meets the requirement of compact structure, convenient assembly and disassembly, easy adjustment, stable performance and less susceptibility to block.