It is targeted to solve the problem of streamline crossover and convergence difficulty in iteration, which is caused due to appearance of a protruded head in computation of the S1 -stream sheet flow field of the axial air compressor with small installing angle, by use of streamline curvature method. A method is proposed, using rotating coordinate to keep the head with leaf-like shape and to hold the relative position of streamlines in flow channel. The method is effectively tested and can be applied to computation and analysis of most axial air compressors.