The invention discloses a method for calculating an optimal cooperation distance of a D2D fusion network based on file popularity. The method comprises the following steps: cell user movement is modeled as random distribution in a spatial Poisson point process, each user caches a video file, the user can obtain the video file by selecting a cellular mode or a D2D mode, the popularity of the video file is simulated by Zipf distribution, a user number ND2D activated by D2D and the user number NBS activated in the cellular mode in a single cell are obtained according to different features of D2D and cellular communication, then a single user obtains the network capacity of the fusion network by the average throughput in the D2D mode and the cellular mode, and a specific application scene and a service demand are obtained by an existing fast iterative algorithm, so the D2D fusion network obtains an optimal cooperation distance d* with the maximum throughput.