Abstract: Centrifugal and axil ventilating fans are optimized by using different objective functions,different variables of design,different constraint forced conditions,different methods of optimization.The results show that they have common features.The effficiency of the optimized design is 5-10% higher than the traditional design.If the static pressure total-effectiveness is chosen as the objective function,the results will be more satisfactory.this procedure of optimization may be modisfied easily to applicable to a blower and a compressor.