To　solve　the　problem　of　the　bad　cooling　performance,　an　experimental　setup　of　the　transcritical　CO2　refrigeration　system　with　an　adjustable　heat　exchanger　is　set　up　in　a　mobile　air　conditioning　calorimeter　facility　to　investigate　the　effects　of　the　internal　heat　exchanger　on　the　performance　and　operation　parameters　of　transcritical　CO2　air　conditioning　system　used　in　electrical　vehicles.　The　experiments　are　conducted　at　the　ambient　temperature　of　35,　38　and　41　with　the　compressor　speed　at　3　500　r/min,　and　the　steady　results　are　measured　under　variable　discharge　pressure　and　heat　flux　of　the　internal　heat　exchanger.　The　effects　of　the　internal　heat　exchanger　on　the　improvement　of　cooling　capacity　and　COP　of　the　system　and　the　influence　on　the　operation　parameters　of　the　compressor　are　analyzed.　The　results　show　that　when　the　exhaust　pressure　is　10　MPa,　the　COP　of　the　system　increases　by　14.2%,　23.3%　and　33.2%　respectively　after　using　the　internal　heat　exchanger　under　the　three　ambient　temperatures,　and　the　cooling　capacity　increases　by　14.3%　to　33.3%.　Meanwhile,　the　pressure　reduction　in　the　heat　loss　was　reduced.　But　using　an　internal　heat　exchanger　would　result　in　the　increase　of　discharge　temperature.　The　higher　the　ambient　temperature　is,　the　smaller　an　internal　heat　exchanger　allowed　is　when　operating　at　same　discharge　pressure.　The　use　of　the　internal　heat　exchanger　can　effectively　improve　the　system　performance,　but　it　will　also　cause　the　increase　of　the　compressor　pressure　ratio　and　the　rise　of　the　discharge　temperature.　So,　the　performance　enhancement　and　the　security　must　be　both　considered　in　the　design　of　the　size　of　the　internal　heat　exchanger　for　a　transcritical　CO2　refrigeration　cycle.　©　2020,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.