IEEEPassive　intermodulation　(PIM)　interference　that　occurs　in　communication　systems　could　limit　the　communication　capacity　and　increase　the　manufacturing　and　maintenance　costs.　In　this　letter,　a　composite　exponential　model　is　developed　to　characterize　the　weak　nonlinearity　of　passive　components　that　causes　PIM　generation　accurately.　This　proposed　model　fully　considers　the　correlation　between　the　PIM　products　on　each　order　and　the　relation　of　PIM　products　with　variation　of　carrier　powers.　For　verification,　a　microwave　filter　is　given　to　demonstrate　the　effectiveness　of　this　composite　model,　and　the　reliability　of　this　model　is　proved　by　the　sensitivity　analysis　due　to　measurement　uncertainty.　Besides,　the　good　agreement　between　the　calculated　powers　of　PIM　products　and　the　measured　data　shows　that　it　can　provide　a　theoretical　guidance　for　PIM　performance　assessment　in　engineering　application,　thereby　evaluating　the　influence　of　PIM　interference　on　communication　quality　effectively.