The invention discloses a mechanism for assisting a rear anchor device in crossing an anchor cable automatically, and belongs to the field of crane auxiliary facilities. According to key points of thetechnical scheme, the mechanism comprises a rear anchor lug seat, a rotary lug seat and a traveling assembly; one end of the rear anchor lug seat is connected with a rear anchor distributive girder,the upper part of the rear anchor lug seat is fixedly connected with a rear anchor girder, and a fixing assembly is arranged at the end, away from the rear anchor lug seat, of the rear anchor distributive girder in a penetrating mode so as to enable the rear anchor distributive girder to be fixed to a main girder; one end of the rotary lug seat is connected with the end, away from the rear anchordistributive girder, of the rear anchor lug seat, and the other end of the rotary lug seat is connected with the rear anchor device so as to enable the rear anchor device to rotate by taking one end of the rotary lug seat as the axis; and one end of the traveling assembly is connected with the rear anchor girder, the other end of the traveling assembly is hinged to the upper part of the rotary lugseat, and the traveling assembly can extend and retract. Through retracting of the traveling assembly, the rear anchor device rotates upwards by taking the rotary lug seat as the axis, thus when conducting traveling construction, a crane can cross an anchor cable device on a braced girder conveniently, the traveling efficiency of the crane is effectively improved, and the construction period of girder erection is shortened.