The invention relates to a bored tunnel variable cross-section stress conversion construction method and belongs to the technical field of tunnel engineering. A profile steel grille local strengthening and transition area grille dense arrangement method is used, profile grilles are used at the cross-section position, the transition section grilles are vertical to the cross section axis and arranged densely and in welding connection with the profile grilles. One profile steel grille is arranged when the 4-4 section is constructed to the crosswire position, 5-5 section grilles are perpendicular to the section axis, the transition area grilles are arranged densely, and the grilles and the profile steel grilles are in welding connection. The 4-4 section profile steel grilles are in welding connection through strengthening plates, and 5-5 section reinforcement grilles and the 4-4 section profile steel grilles are in welding connection. The grilles and sprayed concrete can be attached tightly to surrounding rock, and the sprayed concrete can fill the grilles and space between the grilles and the surrounding rock and can be connected integrally with anchorage rods and forepoling structures, so that the support effect is good.