Within　the　experimental　parameters　of　pressure　of　23-28　MPa,　mass　flux　of　350-1000　kg/(m2·s)　and　heat　flux　of　200-1000　kW/m2,　heat　transfer　characteristics　of　supercritical　water　in　a　2×2　rod　bundle　were　experimentally　investigated.　The　variations　of　circumferential　wall　temperature　distribution　were　obtained,　and　the　reasons　for　this　phenomenon　were　discussed.　The　effects　of　pressure,　mass　flux　and　heat　flux　on　heat　transfer　characteristics　were　investigated　and　the　heat　transfer　deterioration　which　occurred　at　low　mass　flux　condition　was　analyzed.　The　experimental　results　indicate　that　the　circumferential　wall　temperature　is　non-uniform,　the　wall　temperature　in　the　corner　sub-channel　is　the　highest,　whereas　the　central　sub-channel　is　the　lowest.　The　wall　temperature　difference　is　closely　related　to　the　non-uniform　cross-sectional　flow　area.　The　heat　transfer　of　supercritical　water　is　weakened　with　the　increase　of　heat　flux　or　the　decrease　of　mass　flux.　Deteriorated　heat　transfer　occurs　in　the　rod　bundle　when　the　heat　flux　to　mass　flux　ratio　increases　to　a　certain　level.　©　2016,　Editorial　Board　of　Atomic　Energy　Science　and　Technology.　All　right　reserved.