The invention discloses a flexible mineral insulated pre-branch fireproof cable. The fireproof cable comprises a trunk cable. The trunk cable is connected to a branch line cable through a branch connection head. The branch connection head comprises a branch shell. The branch shell comprises an aluminum-alloy upper shell and an aluminum-alloy lower shell. One end of the branch shell is provided with an inlet corresponding to the trunk cable. The other end of the branch shell is provided with an outlet corresponding to the branch line cable. An aluminum sleeve connecting device is arranged in the branch shell. The aluminum sleeve connecting device comprises a copper pressing plate. The copper pressing plate fixes the trunk cable to a U-shaped copper die casting. The U-shaped copper die casting is provided with a branch cable hole corresponding to the branch line cable. And the U-shaped copper die casting is also provided with an insulation puncture device corresponding to the trunk cable and the branch line cable. The branch shell is provided with an insulation glue pouring hole. And the insulation glue pouring hole is provided with a thread sealing port.