Abstract: A new method to control the spreading stream line of blade dynamically on computer screen is proposed in this paper.The Hermite Curve is used to simulate the spreading stream line.The shape of spreading stream line can be adjusted conveniently by moving the mouse.This method combines the quick ability of computer and experience of designer together and makes it possible that the popular blade drawing process known as Equal-Angle Conversion method can be implemented in CAD software.The process of controlling spreading stream line and application example have been given.