Abstract: By using the chemical vapor deposition（CVD）technology，two testing surfaces with gradient surface energy were fabricated on a base of silicon wafer with dodecyltrichlorosilane and octrytrichlorosilane respectively.Using a high-speed video imaging system，the movement of water drop on the horizontal surface with gradient surface energy was visualized and measured under ambient condition.The heat transfer experiments were conducted on dropwise condensation of steam on the surfaces with gradient surface energy.During experiments，the condensing surface was placed at inclination angles of 0°，30°，60° and 90°，respectively.The growth，coalescence，motion，and abscission of condensed droplets were visualized by the high-speed video imaging system.The observed results showed that the condensed droplets larger than about 1 mm in diameter could move at a peak speed of 110 mm·s-1 from hydrophobic side to hydrophilic side on the horizontal condensing surface with gradient surface energy.The velocity of condensed droplet was far larger than that of the droplet on the surface with gradient surface energy in ambient atmosphere.The effects of heat transfer temperature difference，inclination angle of condensing surface，and surface energy gradient on the condensation heat transfer were respectively discussed in virtue of the photographic results.The experimental results showed that with an increase of heat transfer temperature difference，heat transfer coefficient increased to a maximum value and then decreased afterwards.As the inclination angle of condensing surface increased，the condensation heat transfer coefficient increased due to the action of gravity on the departure and motion of droplet.A larger surface energy gradient led to a smaller departure diameter and a faster motion of droplet，which resulted in a larger condensation heat transfer coefficient.