Abstract: A drawing method of plane blade shape using double folium is given. The-characteristics of double folium, the drawing process of blade unfolding picture,the method determining blade thickening and blade boneline inclination of inside and outside circle flow line are describled. Taking FB323 hydrodynamic torque converter for example, working wheel blade designing and computing program and drawing program are programmed. Cycle round shape of hydrodnamic torque converter, unfolding picture and straight projection of inside and outside circle flow line and middle flow line are drawed by computer.Systematizat ion, standardization and computer calculation of blade design method are initially realized.