The invention discloses a transparent crystallization polylactic acid plastic which comprises the following raw materials in parts by weight: 100 parts of polyactic acid, 0.1-5 parts of crystallization nucleating agents, 0.5-20 parts of plasticizers and 0.5-10 parts of other assistants. By adding the crystallization nucleating agents and the plasticizers, the crystallinity, the crystallizing speed and the heat resistance of the plastic are obviously improved, and the crystal nucleus size of the plastic is obviously reduced so that the transparent crystallization polylactic acid plastic has the characteristics of high transparence, heat resistance and tensile strength. The invention also discloses a preparation method of the transparent crystallization polylactic acid plastic, which comprises the following steps of: blending the polyactic acid, the crystallization nucleating agents, the plasticizers and the other assistants, and then carrying out injection moulding to obtain the crystallization polylactic acid plastic. The crystallization polylactic acid plastic prepared with the method can be directly subjected to injection moulding without secondary annealing moulding so that thepreparation method has the advantages of simplicity in operation, strong maneuverability, low production cost and easiness for industrial production.