Observations on the phase transformation of basalt to eclogite were made nader high pressure 50 kb± and temperature 1200-1300℃.Some results about the composition mineral assemblage:pyrope, omphacite, and jadeite are obtained. It is expected to give phase change within a depth in the upper mantle of relevant area, which corresponds to the eclogite facies. There is difference be- tween the two kinds of eclogites in P.-Escola's ACF Diagram. The compositions of Mg and AT increase in our synthetic eclogite with decreasing Ca. At the same time, a vis}us fluid was consisting largely of K, Na, H, C, O, with minute amounts of Si AI, etc. formed only in alkali basalt in the east part of China, while it does not appear in the basalt of Pacific ocean crust, Hawaii and Cali- fornia. A preliminary investigations in comparison between different basalt under high pressure and high temperature, and the study of the crystal cthem- istry in the formation of eclogites and viscous fluid are carried out. Finally, The formation of viscous fluid under specific pressure. and tempe- rature in alkali basalt of China may be regarded as one of the modes of forma- tion of the mantle's asthenosphere. A "Belt" high pressure apparatus was used in our experiments. Vertical depth involved is 150 km in upper mantle,which corresponds to pressure of 5Okb and temperature in the range from 1200 to 1300℃