1. A method of text script generation for a corpus-based text-to-speech system, comprising: (a) searching in a source corpus having L sentences, selecting N sentences with a best integrated efficiency as N best cases, and setting iteration k to be 1, k , L and N being natural numbers, N≦L; (b) for each case n of the N best cases, 1≦n≦N, searching in said source corpus and selecting M k+1 best sentences with the best integrated efficiency from the unselected sentences in said source corpus, 1≦M k+1 ≦L; (c) searching in said source corpus and keeping N best cases out of the total unselected sentences for next iteration, and increasing iteration k by 1; and (d) if a termination criterion being reached, setting the best case in the N traced cases as the text script, otherwise, returning to step (b); wherein said best integrated efficiency depends on a function of combining the covering rate efficiency of unit types, the hit rate efficiency of unit types, and the text script size.