The invention belongs to the technical field of magnesium and magnesium alloy processing, disclosing an application of an aluminium-zirconium-carbon masteralloy in deformation processing of magnesium and magnesium alloys. The aluminum-zirconium-carbon masteralloy comprises the following chemical ingredients in percentage by weight: 0.01-10wt% of Zr, 0.01-0.3wt% of C and the balance of Al. The deformation processing is a plastic molding method. The application is characterized in that the magnesium or the magnesium alloy crystalline grain is refined. Further, the invention discloses a use method of the aluminum-zirconium-carbon masteralloy in the continuous casting and rolling production of the magnesium and magnesium alloy. The invention proposes the application path of the aluminum-zirconium-carbon (Al-Zr-C) master alloy as a crystalline grain refiner in the plastic deformation processing. The aluminum-zirconium-carbon masteralloy has the advantages of strong nucleation capability and good crystalline grain refining effect in the magnesium and magnesium alloys. The magnesium and magnesium alloy deformation materials can be continuously produced on a large scale.