Abstract: Cloud droplets are difficult to be obtained in constructing backward cloud. To slove the problem, a new algorithm using normal interval number was proposed by analyzing the traditional algorithms of backward cloud and in the inspiration of the idea that all fuzzy membership functions could form a curve cluster which could be regarded as an approximation to a cloud.The new algorithm could obtain the cloud droplets by generating some normal numbers in expectation curve and substituting them in each membership function.Experimental results showed that the algorithm could get abundant cloud droplets,which could meet the distribution of normal cloud model.

Key words: normal cloud model, backward cloud, normal interval number, cloud droplets