The invention discloses a track traffic line foreign material invasion limit monitoring device and method. The device mainly comprises an imaging device, a scanning light source device and a control processing unit, wherein the control processing unit is provided with an output and/input interface; the imaging device and the scanning light source device are respectively arranged on respective upright columns at appointed line sides; and an irradiation region of the scanning light source device, an imaging region of the imaging device and an overlapped region of boundary outlines are used as effective monitoring regions. The method comprises a mounting and debugging stage and a real-time monitoring stage, wherein the mounting and debugging stage comprises the steps of: (1) equipment mounting; (2) equipment debugging; and (3) standard data collecting; and the real-time monitoring state comprises the steps of: (4) data obtaining; (5) real-time processing; (6) invasion limit alarming; and (7) circulated execution of steps (4)-(6). The track traffic line foreign material invasion limit monitoring device and method have the following advantages of simple and reasonable device, scientific and reasonable method, capability of reducing monitors and obtaining foreign material invasion information in time, and convenience for timely confirmation and foreign material removal.