Beijing,　Shijiazhuang　and　Tangshan　were　selected　as　the　typical　cities　in　the　Beijing-Tianjin-Hebei　region　to　investigate　the　seasonal　variation　characteristics　of　secondary　water-soluble　inorganic　ions　and　compare　the　pollution　characteristics　and　physicochemical　property　of　the　secondary　water-soluble　ions　between　heavy　pollution　period　and　other　periods.　Then　CAMx-PSAT　model　was　applied　to　quantitatively　analyze　the　contribution　on　PM2.5　and　SNA　concentration　from　pollution　sources　in　BTH　region　during　different　seasons.　Results　showed　that　PM2.5　concentration　in　these　cities　decreased　year　by　year,　and　the　maximum　of　SO42-,　NO3-　and　NH4+　concentration　mostly　in　winter　at　the　same　time,　illustrating　the　related　correlation　of　their　concentrations.　The　mass　concentrations　of　SO42-,　NO3-　and　NH4+　increased　significantly　during　heavy　pollution　period　compared　with　other　periods.　The　largest　concentration　ratio　of　SNA　appeared　in　1~2　days　before　heavy　pollution　days.　The　formation　of　heavy　pollution　was　the　combined　effects　of　local　pollutant　emission　and　external　source　region　transport.　The　contribution　of　external　sources　to　NO3-　was　higher　than　that　of　SO42-　and　NH4+.　In　addition,　the　concentration　of　PM2.5,　SO42-　and　NO3-　were　mostly　contributed　from　traffic　sources,　resident　sources　and　industrial　sources,　and　the　resident　sources　were　the　most　important　contributor　for　NH4+　concentration.　©　2018,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.