The satellite signals of multi-UAV systems are susceptible to interference in complex environments. To address this issue, a cooperative navigation method based on loop sum-product algorithm is proposed. According to sensor′s characteristics, the absolute navigation based on the GNSS / INS tight combination and UWB-assisted satellite double-difference tight combined relative navigation are designed. Each platform′s absolute navigation information and relative navigation information between platforms are used to construct a collaborative navigation filter. Message transmission rules are designed to reduce the flow between platforms based on loop sum-product algorithm. Calculation tasks are distributed and run on each platform, which reduces calculation pressure. Finally, simulation and UAV experiments are carried out for different complex scenes. Results show that this scheme′s cooperative navigation accuracy is significantly better than the result without cooperative navigation. With the increase of observable information, this method′s navigation accuracy is getting higher and higher.