The invention discloses a die locking device for directly extruding a casting die. The die locking device comprises an upper die locking ring and a lower die locking ring, wherein the upper die locking ring is arranged at the outer part of a right side die in a sleeving way, the lower die locking ring is arranged at the outer part of a left side die in the sleeving way, an annular inner surface of the upper die locking ring and the lower die locking ring is in a consistent angle with a conical surface of a mould assembling position of the left side die and the right side die, the left side die and the right side die can be mutually matched during mould assembling, and a self locking angle can be formed. When the left side die and the right side die are in the mould assembling in advance, the lower die locking ring moves to a side die lower mould assembling position under the driving of a lower die locking ring driving cylinder and is subjected to self locking, and the upper die locking ring moves to a side die upper mould assembling position under the driving of an upper die plate and is subjected to the self locking; a side die is locked after the upper die locking ring and the lower die locking ring reach the mould assembling position, a sealed cavity is formed by the upper die locking ring, the lower die locking ring, the side die, an upper die and a lower die together, and die assembling and mold filling are realized; after the mold filling, the upper die moves downwards for pressurizing, a connecting screw rod on the upper die locking ring returns to an upper die plate hole, movement separation of the upper die locking ring and the upper die is realized, and a die locking force during an extruding process is provided by the upper die locking ring and the lower die locking ring together.