Abstract: Cloud model is an effective tool in uncertain transforming between qualitative concepts and their quantitative expressions. Based on the theory of probability statistics， the authors make the more thorough research to the property of normal cloud， and construct a new algorithm of backward cloud which is more precise than the old one. Finally， a simulation is given to compare the new algorithm with the preceding twos.

Key words: cloud model, forward cloud, backward cloud, least squares

摘要： 云模型是一种可以有效地实现语言值表示的定性概念与其定量表示之间不确定性转换的模型。文章对正态云作了较深入地概率统计分析，指出了现有逆向云算法的不足，并提出了一种新的精确度更高的逆向云算法，最后通过模拟实验比较了新算法与原逆向云算法。

关键词: 云模型, 正向云, 逆向云, 最小二乘