The primary sensitive factor that the thermal power units consider in four pipes design is the resistance by using bend or elbow. The divergence existing in resistance calculation of bend and elbow is clarified according to the U.S.Crane Co. manual which is the source of disputation and perplexity. It is demonstrated by comparisons that energy saving and resistance reducing are very obvious and the project cost is reduced by replacing elbow with bend, worthy of popularization in four pipes design. It is also shown from the access rules of resistance coefficient based on the Crane regulations that energy saving and resistance reducing exist theoretically in designing four pipes.