Abstract: Fracture density is an important parameter for reservoir evaluation. This paper proposed a new method for calculating fracture density by using the anisotropic gradient. Firstly fractured medium is equivalent to the anisotropic HTI medium with the equivalent theory, then the AVO attributes of fractured medium were obtained so as to calculate the anisotropic gradient of fractured medium; finally the fracture density of fractured medium was got based on the relationship between the anisotropic gradient and fracture density. In the actual processing we can obtain the anisotropic gradient from the seismic data and then get the fracture density. The numerical examples suggest that we can get the accurate fracture density of the fractured medium by the method in the present study. The inversion results are consistent with the initial model, verifying the correctness of the method. In addition, we can also get the fracture density from the seismic data with noise, suggesting the stability of the method.