This paper deals with the exper imental Study on the heat transfer per formance about a single miniature thermosiphon pipe. The results show that: the two- phase flow pattern and its transfo rm gr eatly affect the pipe sur face temperature dur ing the heat pipe running. T he heating source temperature has some effect on the flow patter n change; the hig her the heating source t emperatur e, the smaller t he temper ature difference along t he condensing section of the pipe. The pipe length also affects the surface temper ature especially at the low heating sour ce temperatur e. Tthe surface temperature will increase as the lengt h of heating section becomes longer, and there is nonlinear relation between the heat transfer pow er and the heating source temperature.