To　evaluate　the　effect　of　phase　change　materials　(PCMs)　on　the　indoor　thermal　environment　of　greenhouses　under　different　weather　conditions　and　over　a　long　time　in　the　heating　season,　a　study　was　carried　out　using　both　experimental　method　and　numerical　method.　The　study　was　conducted　in　a　typical　greenhouse　located　in　Beijing,　China,　and　important　parameters　have　been　monitored　continuously　for　61　days,　including　indoor　air　temperature,　outdoor　air　temperature,　solar　radiation,　surface　temperature　of　greenhouse　envelopes　and　soil　temperature.　Based　on　these　parameters,　a　number　of　indicators,　namely,　operative　temperature,　daily　effective　accumulative　temperature,　irradiated　surface　temperature　of　the　north　wall,　average　temperature　of　PCMs,　and　daily　heat　storage　and　release,　have　been　used　to　evaluate　the　performance　of　PCMs　in　greenhouses.　All　indicators　have　provided　consistent　results　that　confirm　the　positive　effect　of　PCMs　on　improving　the　indoor　thermal　environment　of　greenhouses　over　a　long　time.　Additionally,　the　paper　has　demonstrated　that　a　sunny　weather　could　help　to　promote　the　efficiency　of　PCMs,　comparing　to　a　cloudy　weather.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.