The invention relates to a method for preparing for medium slab continuous casting, and belongs to the technical field of continuous casting production in the metallurgical industry. According to thetechnical scheme, a gap between the inner wall of a crystallizer (8), a dummy bar head (6) and a dummy bar head cushion block (5) is plugged by an asbestos rope, and a cooling steel plate (10) with the thickness of 0.5-1.5 mm is flatly laid at the bottom of the dummy bar head (6); the asbestos rope surface between the crystallizer (8) and the dummy ingot head (6) is covered with strip-shaped cooling steel (12) with the length of 100-150 mm, the width of 10-30 mm and the thickness of 1-2 mm, and cooling flat steel (11) with a certain weight is put on two sides of the dummy ingot head (6); and fiber blankets (9) with the width matched with that of a narrow copper plate (1) of the crystallizer are respectively placed on two sides of the narrow copper plate (1) of the crystallizer. The methodhas the beneficial effects that the waste cold plate trimming is adopted to replace traditional standby material springs and iron scraps, so that the production cost is saved, and it is ensured that the continuous casting starting success rate can be 99.9%.