The diameter of semi-round pipe is Φ100mm. Bending radius of semi-round elbow is R100mm. It is too minor to adopt traditional way of elbow forming. The bending dies and billets were designed through analysis and theory calculation. The structure of dies and billet was optimized through bending experiment .The wrinkle and cracks were avoided. The spring back was controlled. The regular semi\|round elbow was made out.