An　outdoor　air　quality　monitoring　system　based　on　ZigBee　wireless　sensor　network　is　presented　in　this　paper.　A　wireless　network　is　formed　by　coordinators,　routers,　terminal　notes,　and　especially　PPB　(part　per　billion)　level　high　precision　sensors.　Data,　sampled　and　processed　by　terminal　notes,　are　sent　to　routers　or　the　coordinator　through　a　serial　port,　then　displayed　on　a　screen　of　a　Pc.　The　concentration　of　CO,　SO2,　O-3,　NO2　and　NO　in　the　air　can　be　observed　online　in　real　time.　System　architecture,　hardware,　and　software　are　implemented　based　on　ZigBee　wireless　sensor　network.　The　whole　system　has　high　precision,　low　cost,　and　low　power　consumption.　Also　different　sensors　can　be　connected　to　network　for　extended　functions　and　various　fields.