The　synthesis　of　a　low　dielectric　constant　polyimide　(PI)　with　a　polyhedral　oligomeric　silsesquioxane　(POSS)　cross-linked　structure　is　presented.　A　non-planar　conjugated　diamine　monomer　(FSNH2)　with　two　-CH=CH2　reactive　groups　was　first　synthesised　in　a　two-step　process,　and　then　two　polyimides　were　synthesized　by　PSS-Octavinyl　(OVPOSS)　substituted,　FSNH2　and　dianhydride.　OVPOSS　cross-linked　polyimides　have　good　thermal　stability　and　low　dielectric　constant.　6FDA-FSNH2-OVPOSS(6FPI-3)　can　reach　a　minimum　dielectric　constant　of　2.08　(108　Hz)　and　a　dielectric　loss　of　0.008　(108　Hz).　In　addition,　the　cross-linked　structure　of　the　OVPOSS　and　polyimide　chains　prevents　the　agglomeration　of　OVPOSS　to　a　certain　extent　and　improves　the　tensile　strength　and　elongation　at　break　of　the　polyimides,　which　has　great　application　potential　in　large-scale　integrated　circuits.