The invention discloses a heading mechanism of a cantilever type heading machine, which is characterized in that five motion branch chains are respectively a parallelogram motion branch chain (3) and four linear-moving motion branch chains (4, 5, 7 and 8) with the same structure. In the parallel quadrangle motion branch chain (3), four connecting rods (14, 15, 18 and 19) are respectively coupled with four rotating pairs so as to form a parallelogram mechanism; the connecting rod (19) is coupled with a base seat (1) through a rotating pair (13); and the connecting rod (15) is connected with a rotating shaft (16) which is vertically arranged on a cutting arm (10) through a rotating pair (17). The linear-moving motion branch chains (4, 5, 7 and 8) are liner-moving driving rods; one end thereof is coupled with the cutting arm (10) through a spherical hinge and the other end thereof is coupled with corresponding pillars through a hook joint; and the base seat (1) is fixedly connected on a travelling mechanism (12). By the expansion of the four linear-moving driving rods (4, 5, 7 and 8), the horizontal swinging, the vertical swinging, the back and forth motion and left and right motion can be realized. The invention has the characteristics of simple structure and being capable of realizing smooth profile and the like, is an ideal heading mechanism of the cantilever type heading machine and can be applied to the fields of excavating coal in coal mine and semi-coal and rock laneways.