North　China　is　recognized　as　one　of　the　region　with　most　severe　air　pollution　in　China,　and　the　PM2.5　in　six　major　cities　(Beijing,　Tianjin,　Shijiazhuang,　Taiyuan,　Jinan　and　Zhengzhou)　of　this　region　was　measured　to　be　108.7-186.0　mu　g　m(-3)　in　January　2017　and　39.2-56.3　mu　g.m(-3)　in　July　2017.　This　study　conducts　the　meteorological　and　chemical　simulations　based　on　WRF-Chem,　and　explores　the　impacts　of　meteorology　and　emissions　on　PM2.(5)　(particulate　matter　with　aerodynamic　diameters　＜=　2.5　mu　m)　pollutions.　Simulations　show　a　noticeable　seasonal　variation　in　planetary　boundary　layer　height　(PBLH)　and　relative　humidity　(RH),　but　a　similar　trend　in　wind　speed　(WS).　Compared　to　PM2.5　good　condition　(＜=　75　mu　g　m(-3)),　daily　PBLH　decreased　by　7.6-39.6%　in　January　and　9.2-44.1%　in　July　during　PM2.5　polluted　condition　(75　similar　to　150　mu　g　m(-3)),　and　by　22.3-51.2%　in　January　during　severely　polluted　condition　(＞150　mu　g　m(-3)).　PBLH　is　thought　of　as　the　key　factor　for　PM2.5.　Then,　the　synergy　between　PBLH　and　other　meteorological　factors　are　studied.　For　a　100　m　failing　in　PBLH,　the　decrease　in　surface　WS　reaches　0.2-0.8　m　s(-1)0.1-0.3　m　s(-1)　in　January　and　July.　It　means　a　synergic　effect　of　unfavorable　horizontal　and　vertical　dispersions,　more　adversely　in　January　than　in　July.　While,　RH　presents　an　increasing　trend　with　PBLH　falling,　about　+2.1　similar　to+3.2%　in　January　and　+2.7　similar　to+4.6%　in　July　per　100　m　falling　in　PBLH.　Considering　the　improvement　of　high　RH　in　heterogeneous　chemistry　to　form　the　secondary　PM2.5,　we　believe　that　the　disadvantaged　dispersion　condition　is　always　accompanied　by　enhanced　secondary　PM2.5　formation　chemistry.　Then,　we　summarize　the　average　simulated　PM2.5　under　various　combinations　of　PBLH,　WS　and　RH,　and　find　that　under　the　same　meteorological　combination,　PM2.5　in　January　was　about　1.7-3.6　times　that　of　July,　which　could　be　explained　by　the　more　emissions　of　PM2.5　and　its　precursors　in　January.　Finally,　we　determine　the　unfavorable　meteorology　condition　based　on　current　regional　emissions　and　China＇s　standard　(hourly　PM2.5　＜75　mu　g　m(-3)),　low　PBLH　(＜600　m)　or　middle-high　RH　(＞40%)　for　January,　high　RH　(＞60%)　&　low-middle　WS　(＜4　m.s(-1)),　or　middle　RH　(40　similar　to　60%)　&　low　PBLH　(＜400　m)　for　July.　These　unfavorable　meteorological　conditions　accounted　for　75.8%　in　January　and　47.8%　in　July.　Therefore,　it　is　still　necessary　to　continuously　reduce　anthropogenic　emissions　in　this　region　for　attainment　of　China＇s　PM2.5　standards.