Abstract: For the mechanical seal applied in the high speed turbo pump and taking 15^# hydraulic oil as sealing medium, the experimental research on thermal change was carried out by a high speed seal test rig considering the factors (e.g. circulation cooling quantity, rotational speed, media pressure and friction pairs). The results show that the face temperature of mechanical seal was sensitive to all of above-mentioned factors. The face temperature increased linearly with increasing rotation speed. There was a threshold value of circulation cooling quantity for the face temperature and it is recommended that the circulation cooling quantity took a 120% of the threshold on practice works. Medium pressure had obvious influence on the face temperature, but was not as much as the rotational speed. To obtain low face temperature as far as possible, it is advisable to use impregnated resin graphite as stator instead of ordinary graphite and to use silicon carbide as rotor rather than molybdenum alloy.