Abstract: The low-altitude economy （LAE） is expected to drive the large-scale deployment of low-altitude applications in fields such as transportation， environmental monitoring， agricultural production， and cultural entertainment， while generating remarkable economic and social value. As a key enabling technology for sixth-generation mobile communication， integrated sensing and communication （ISAC） is recognized as an important technical pathway to supporting the development of the LAE. Benefiting from the advantages of high-altitude deployment and high mobility， using an unmanned aerial vehicle （UAV） as an aerial base station to provide ISAC services for both ground and aerial users can effectively enhance the coverage capability of communication and sensing. However， traditional monostatic ISAC systems perform signal transmission and echo reception simultaneously on the same device， making them vulnerable to severe self-interference， which significantly impairs the performance of both the communication and sensing functions. To address these issues， this study investigates a multi-UAV-ISAC system for cooperative target localization and communication， in which distributed sensing UAVs cooperatively transmit ISAC signals to a central UAV， enabling centralized processing of sensing echoes. Based on this system architecture， this study derives the Cramer-Rao lower bound （CRLB） for distance estimation in cooperative target localization， and formulates an ISAC-UAV selection problem for CRLB minimization under the constraints of the UAV cooperation cost and communication signal-to-interference-plus-noise ratio （SINR）. Based on this approach， a symbol-level fusion method for multi-UAV sensing information is designed， which effectively improves the cooperative sensing accuracy by performing weighted fusion on the symbol information matrices of multiple UAVs. Numerical simulation results verified the significant advantages of the proposed multi-UAV-ISAC cooperative sensing scheme in target localization. The findings provide a theoretical basis and practical reference for the design and deployment of large-scale UAV swarm cooperative sensing systems.