Supercritical　fluids　have　a　wide　range　of　applications　in　ultra-supercritical　power　units,　water　cooled　reactors　and　aerospace　fields　with　a　good　performance　in　flowing　and　heat　transfer.　When　medium　works　in　large　specific-heat　region,　a　dramatic　change　in　physical　properties　of　fluids　occurs,　resulting　in　a　complicated　change　about　the　flow　structure　in　tubes.　In　the　present　paper,　the　main　conclusions　are:　At　supercritical　pressure,　when　the　water　works　in　large　specific-heat　region,　the　frictional　resistance　coefficient　values　decrease　sharply,　leading　to　a　lower　friction　pressure　drop　and　a　smaller　proportion　in　total　pressure　drop;　simultaneously　acceleration　pressure　drop　values　gradually　increase.　At　low　heat　flux,　the　heat　transfer　coefficients　are　in　good　proportions　to　acceleration　resistance　coefficients.　An　appropriate　increase　in　heat　flux　could　effectively　enhance　the　heat　transfer　coefficients.　At　high　heat　flux,　being　accompanied　with　heat　transfer　deterioration,　a　big　velocity　and　viscosity　gradient　difference　exist　and　laminarzation　phenomenon　occurs　at　the　same　time　in　tubes.　The　heat　transfer　mechanisms　of　supercritical　water　has　been　analyzed　in　this　paper.　Whether　the　heat　transfer　is　improved　or　deteriorated　primarily　depends　on　the　extent　of　the　difference　of　physical　properties　of　fluids　in　different　radial　positions.　©　2015　The　Japan　Society　of　Mechanical　Engineers.