Abstract: The words library is an important data structure in the word input processing of Chi- nese information processing system.The performance of the whole system depends directly on the reasonableness of design for its structure.This paper firstly offers a descriptive method for this per- formance and the multilevel words library structure.By analyzing the performance,the important infl- uence of the words library on the system response time is then pointed out.Finally,the elimination algorithms and self-defining words technique are discussed.