In the application of 3D data visualization, demands on insight into the inner region-of-interest (ROI) of volume are often made while keeping the outer tissue visible. However, a better effect is usually achieved after 3D data has already been preprocessed. In this paper, according to the traditional optical model of volume rending, an interactive optical model is deduced. The calculations on the transmitted light effect of 3D data are introduced in the classifying information. And a perspective ray model based on inner region of interests is constructed. In this model, a better perspective effect is gotten without any preprocessing while keeping the outer tissues semi-transparent. The experiment proves that this method produced a more intuitive result than the traditional model together keeping the frame rates greater than 20 f/s. Using this model, the ability to recognize the feather of 3D data is improved and the theoretic supports are provided for the effective analysis on 3D data.