Abstract: In order to investigate the factors influencing the cross-sectional distortion of small-radius dieless hot-bending bend and grasp the influential laws of technological parameters on the size of the cross section, so as to optimize and control the geometric deformation of the cross-section of small-radius pipe bend and reduce the distortion, the relationships between the processing technological parameters (heating temperature, advance speed and bending radius) and the cross-sectional distortion parameters (wall thinning ratio, wall thickening ratio and ovality) of L415M small-radius (3 D) pipe bend (pipe diameter is 610 mm, wall thickness is 11 mm) were analyzed to reveal their correlation. It is showed that the bending radius of pipe bend has the remarkable effect on the cross-sectional distortion, and the shorter the bending radius is, the more serious the cross-sectional distortion is. As the advance speed increases, the wall thinning ratio and ovality of the pipe bend decrease, and the wall thickening ratio increases. And with the increase of the heating temperature of pipe bend, the wall thinning ratio and ovality of the pipe bend increase, and the wall thickening ratio decreases. The research results can provide technical reference for the design and processing of small-radius hot-bending bend.