The invention discloses a transition line section tunnel CRD (Cross Diaphragm) construction method. The tunnel face outside the range of core soil of upper bench is closed by C20 concrete (50mm in thickness), before the grouting of the advanced small pipes in each row. A locking anchor pipe is arranged at a steel frame joint, and the anchor pipe is a steel perforated pipe shown in the description,where L is 2.0m. The front-back staggered space between pilot tunnels is not less than 10m, and the specific staggered length is adjusted appropriately according to the cross section length. Residuesbelow the foundation must be cleared before mounting the steel frame, the overexcavation part is filled properly by sprayed concrete, then the steel frame is located on the sprayed concrete cushion layer, so as to prevent overall sinking of the steel frame or sinking of the two non-uniform sides. the running tunnel excavation footage is equal to the grille space; a civil defense section, a transition line section 1, a transition line section 2 and a transition line section 3 are subjected to CRD construction; each pilot tunnel is built by the benching tunneling method; the construction is carried out under the principles of advanced pipe, strict grouting, short footage, strong support, early closing and frequent measurement', thereby guaranteeing safe and smooth tunnel construction.