In view of the relative positioning requirements of massive UAV cluster in the GNSS rejection environment, firstly, a relative positioning method is studied based on ranging in the UAV cluster Ad-hoc network. The generalized distance square matrix is constructed by the ranging information of the Ad-hoc network, and then the relative positioning results are obtained after the two-center processing and eigenvalue decomposition. Finally, the positioning accuracy of this proposed method under different ranging errors and UAVs quantity is evaluated by simulation. Results show that, the ranging error is the critical factor that affects the positioning performance. When the cluster is greater than 30 UAVs, the positioning error is relatively less affected by UAVs quantity.