Due to the absence of incident direction and azimuth direction seismic information in post-stack seismic data, conventional post-stack methods cannot use anisotropic variation characteristics to predict fractures. The response of heterogeneous fracture wave field is bidirectional in both incident direction and azimuthing direction, and its response is weak. Generally, it is hidden in the strongly reflected wave field information, and its sensitivity is not easy to be detected by conventional prestack fracture prediction method. The application effect of conventional prestack fracture prediction method is not ideal, and fracture is one of the difficulties in seismic prediction. Therefore, a 3D prestack fracture prediction method based on azimuthal radially-split gradient variation is developed in this paper. The 3D prestack seismic response amplitude equation based on azimuthal impedance factor and azimuthal anisotropy factor varying with the incident angle is derived, and based on that, the quadratic function of 3D prestack seismic response amplitude of one-variable with the sine square of the incident angle is derived at a certain azimuthal angle, and then, the derivative is taken and it gives a first order amplitude gradient equation of one-variable with the sine square of the incident angle, it is proved that the variation of the fixed azimuthal amplitude gradient is linear, the azimuthal anisotropy factor is the main factor leading to the variation of fixed azimuthal amplitude gradient, and its influence enhances with the increase of incident angle, the larger the incidence angle, the greater the anisotropy effect. It is proved that the amplitude variation with incidence-angle in fixed azimuthal direction has piecewise partitioning property, and the amplitude gradient values of different sections can be obtained by linear partitioning of the incident area, and then the amplitude gradient variation with azimuthal change can be used to predict stratum fracture with 3D prestack seismic gather. A new prestack crack prediction software is developed by programming the theoretical method of this paper. Good application effect has been achieved in the actual work area. The results show that this method is accurate and reliable, it can solve the problem of stratum microfracture prediction, and it can provide strong support for the exploration and development of complex fracture reservoirs.