The main hole of the Chinese Continental Scientific DrillingProject (CCSD) with a target depth of 5 000 m is located in the southern segment of the Sulu ultra-high pressure (UHP) metamorphic belt in central eastern China. Nearly continuous core samples from the depth interval of 0～2 050 m are UHP metamorphic rocks consisting of eclogite, paragneiss, orthogneiss (granitic gneiss) and garnet peridotite. In-situ laser oxygen isotope analyses of UHP minerals from drill cores indicate that the δ18O values ranging from -6.8 ‰ to +7.5‰gradually decrease from the surface to the depth of 1 100 m and then increase with the increasing depth. Late Proterozoic granitic intrusion (orthogneiss) occurring at the depth interval of 1 100～1 600 m must have been a heat source for the fluid_rock interaction between the supracrustal rock and the low oxygen isotopic meteoric water. Therefore, an extremely intense interaction between the granitic body and the country rock at the contact zone produced the lowest oxygen isotopic value in adjacent eclogite. Most UHP minerals show equilibrium oxygen isotopic compositions at a centimeter-scale. Peak-UHP metamorphic temperatures are estimated at 700～882℃ by the oxygen isotopic thermometer. Deformation and different degrees of recrystallization during syn-UHP metamorphism and post-UHP retrogression as well as related local fluid interaction may be the main factors responsible for oxygen isotopic disequilibrium between UHP and retrograde minerals. Studies also demonstrate that the extremely low_oxygen isotopic compositions of UHP minerals were preserved during the subduction and exhumation of the continental plate, and large-scale fluid flow did not occur during the pre-, syn-, and post-UHP metamorphism. Garnet-peridotites nearly 80 m thick are in tectonic contact with supracrustal rocks and have oxygen isotopic values of normal mantle rocks.This suggests that, in contrast to the deeply subducted supracrustal rocks, the ultramafic rocks are a tectonic slice derived from the mantle wedge above the subduction zone and have not been subjected to the hydrothermal alteration with the low oxygen isotopic meteoric water.