Problem of disagreement between 2-D drawing and actual wood former of double-channel impeller of sewage pump most possibly encountered if the design is from traditional 2-D manner. Research was carried out for the method of 3-D design directly in Pro/ENGINEER, so 2-D drawing could be produced by projecting through 3-D impeller designed. The procedure could secure the agreement between 2-D drawing and actual wood former. A practical design exemplified the correctness of the method by experiment. Additionally, a formula was deuced, which showed the relation between the outlet angle of center line of channel and wrap angle, variant coefficient, if archimedes spiral was assumed as the curve of center line of plate plane. It was the basis to control outlet angle of channel. Another formula was presented for the calculation of normal distance from points on the passage center line to outer diameter and formula of cross-section area as outlet point was also available. Based on them, a new method was developed for fin，ding out the outlet point.