In this paper, in terms of the variational principles and the boundary-layers theory, a numerical method of flow fields through cascades is presented. The velocity and pressure fields of potential flow are offered. The characteristic parameters of boundary-layer, frictional and total loss coefficients are also given. The calculating results ars closely in agreement with the experiment data of the manufactural plant. The present computational method and program can be used directly to the calculation of the cascades on arbitrary streamsheet of revolution in centrifugal and axial turbomachines. They can answer such important questions as how to obtain the minimum loss coefficient and the best possible efficiency.