Abstract: A composite down-hole catalytic viscosity reduction technique,integrated with functions of viscosity reduction by surfactant,hydrothermal cracking and catalysis and oxida- tion catalysis,was invented to mobilize the extremely dense oil reserves.The technique has been used successfully in 6 wells with extremely dense oil in Henan oil field.Analysis shows that the physical properties of crude oil are improved apparently,for the heavy components are decreased while the light components are increased.The average oil yield of individual well is increased by 12.5 t.