A 3D image generation method includes controlling a G-arm frame to rotate to a target angle, and keeping the currents and voltages of two X-ray tubes unchanged during rotation, obtaining groups of 2D projection data of an object when a G-arm is in different angles, each group of 2D projection data including two paths of projection data, conducting calculation according to an FDK algorithm or an FDK correction algorithm using the groups of 2D projection data to obtain a 3D image of the object, and outputting the 3D image, thereby greatly reducing the data obtaining time by obtaining two paths of projection data, effectively reducing the irradiation time of the object, directly outputting the 3D image of the object, reflecting the full view information about the object, and solving the problem in the prior art that the irradiation time of the object under examination of X-rays is long.