The invention discloses a splitting active oral cavity mouth gag, which comprises an upper jaw plate, a lower jaw plate, upper and lower L-shaped force transfer rods, and an elastic restoring member, wherein the upper and lower L-shaped force transfer rods are fixedly connected in the middle of the upper jaw plate and the lower jaw plate, and the elastic restoring member is arranged between the upper and ; when in use, the upper jaw plate and the lower jaw plate are respectively worn to stabilize and are positioned on an upper dental arch maxillofacial and a lower dental arch maxillofacial; an elasticity rubber ring is hung on a small hook of the upper and lower force transfer rods; the amount of the rubber rings to be hung is adjusted according to the order of severity of the limited individual opening; and the shrinkage force that the rubber ring is extended achieves the function of continuously opening through the force transfer rods. The splitting active oral cavity mouth-opener has the advantages of small volume, convenient wearing and simple operation, can make a mouth-close movement of the mandible when worn, and can enable the function of the masticatory muscles to acquireeffective practices; the size of the mouth opening force can be adjusted through increasing and decreasing the rubber ring; the engagement surface of the jaw plates are matched with the occlusal surface of patients and encircled by a buccal fin so as to acquire a stable fixed position. The splitting active oral cavity mouth gag can be used for computer assisting design of individual repairing body of the maxillofacial part.