The invention discloses an anchored roadbed widening method, which belongs to the technical field of road construction. The anchored roadbed widening method comprises the following steps of: firstly performing slope cutting on an old roadbed slope, then excavating a step on the old roadbed slope from the ground, obliquely drilling an anchorage hole into an old roadbed at the joint of the vertical plane of the step and the horizontal plane, placing a steel bar into the anchorage hole, and casting the steel bar and the old roadbed into a whole by pouring cement grout; laying a new roadbed in layers, rolling, flatly laying a geogrid on the step of the old roadbed when the new roadbed is filled to be aligned with the step of the old roadbed provided with the anchorage drilled hole, connecting a transverse rib of the geogrid with an end hook which is bent upwards of the exposed part of the steel bar, tensing the geogrid, fixing with the lower layer of a soil body, and finally filling soil on the geogrid and rolling. According to the anchored roadbed widening method disclosed by the invention, an anchor rod technology is used for reinforcing the old roadbed slope, the geogrid and the old roadbed are connected into a whole, the geogrid can be prevented from sliding on the step of the old roadbed, the stability of the new roadbed and the old roadbed is improved, and non-uniform sedimentation can be effectively controlled.