<p>As a foundational configuration of spatial tubes, the spiral metal tube has been widely used in the industrial tube line system. Unfortunately, its precise forming remains a challenge up till now. In this paper, an improved analytical model is presented to reveal the forming mechanism of the spiral tube taking various processing parameters into account and verified by the FE simulations and four-axis free-bending (FFB) bending experiments. The method of springback prediction for the spatial configuration is given, and the transformation between four-axis and six-axis free bending process is provided. The conclusions can be drawn that the curvature radius primarily decreases with the increment of the offset, and the pitch mainly diminishes with the growth of the ratio defined as pushing velocity versus angular velocity of the panel. When the ratio is constant, the forming result remains unchanged, which is consistent with the theoretical model. Meanwhile, the evolution mechanism of forming quality is explored to provide a certain reference for the actual forming process. For the same tube configuration, reduction/thickening of wall thickness and cross-section distortion can be improved with the synchronous increase of the ratio of pushing velocity and angular velocity. It was innovatively found that the nonuniform distribution of shear stress under lower loading velocities is the dominant reason for the lower forming quality. This research effectively reveals the spiral tube forming mechanism and the evolution mechanism of forming quality, which establishes the foundation for analyzing the forming issues of complex spatial tubes in this field.</p>