Abstract: The Diffusion Factor Flow-Type Design (DFFTD) is a new design method with inequable work along the radius of the blade in compressors. This method gives the designers a great pull to design, thus the capacity of work done by blade can fully be developed, the limits of load can reasonably be controled, the coeffiicient and the operating range of impeller are increased and expanded respectively. Further investigation about application of DFFTD for Axial and Mixed-Flowcompressors has been made in this paper. The computing programs of DFFTD presented bythis author are Simpler and gratifyingly accurate, so it can directly employed in actual engineering design. On the basis of this author's recent works, the choosing of ,distribution of diffusion factor is more deeply described, the matching between the distribution of diffusion faetor and Clu (r1) is analysised by comparison and calculation, moreover, the affect of Curvature term and its sensibility on result are in detail discussed to enlarge applicable region of DFFTD. It is obvious that to completely solve the choosing of the distribution of diffusion factor, the optimal problem of DFFTD must be established. The theoretical analysis and the computing results shows that the exact optimal solution can be yielded by mean of Modern Optimizational Control Theory. This computing method and program of optimal problem is applicated in engineering problems and developed to optimizing of other Flow-type Designs.