In　the　paper,　the　formation　control　problem　in　unknown　environments　for　networked　multi-unmanned　aerial　vehicle　systems　(UAVSs)　is　resolved　under　a　nonlinear　differential　game　(NL-DDG)　framework.　The　main　challenge　of　this　framework　is　how　to　obtain　feedback　Nash　strategies,　which　typically　overly　rely　on　global　information　and　cannot　ensure　the　existence　of　Nash　strategies　in　unknown　environments.　Toward　this　goal,　we　initially　design　collision　avoidance　rules　to　ensure　the　safety　of　each　UAV.　Subsequently,　we　utilize　an　inverse　optimal　control　method　to　construct　the　NL-DDG　that　incorporates　both　formation　control　and　collision　avoidance　costs,　enabling　the　derivation　of　analytical　forms　of　Nash　strategies　relying　solely　on　local　information　and　minimizing　performance　metrics.　In　addition,　the　existence　of　feedback　Nash　strategy　can　be　guaranteed　with　an　undirected　and　connected　information　topology,　which　represents　the　optimality　for　the　UAVSs.　Moreover,　we　analyze　the　stability　of　the　closed-loop　system.　Finally,　the　simulation　results　validate　the　effectiveness　of　the　proposed　scheme.