No, it refers to tomorrow. The sentence can be rephrased as follows: "Prepare for what will happen tomorrow on the night before tomorrow (i.e. tonight)".
Thank you. Of course "tonight" is understandale. The problem is that the original sentence used "the night before." The tonight's tomorrwo is tomorrow, while "the night before's tomorrow" is yesterday. For example, at present in China the time of tonight is 10:00PM of March 12 right now, so tonight's tomorrow will be March 13. The night before should the night of March 10,