Abstract: In response to the less-than-satisfactory results of microbial, hydrothermal catalysis and gas-assisted viscosity reduction methods during the mid-to-late stages of production in shallow ultra-heavy oil reservoirs in Fengcheng, a study on the technology of catalytic modification and viscosity reduction for ultra-heavy oil was conducted. Using oil samples from wellblock Chong-18 in Fengcheng Oilfield, the viscosity reduction effect of catalyst and hydrogen supplier at 4.5 MPa and 100-220°C was analyzed through catalytic cracking experiments. Additionally, the effect of catalytic modification agents on steam-assisted displacement and the changes in crude oil composition were analyzed by using a dual-tube parallel oil displacement experiment. The results show that the viscosity reduction rate using the catalyst alone could reach 50%, while exceed 90% when combined with a hydrogen supplier, at 220°C. In the single-tube steam flooding experiment, the viscosity reduction rate reached 88%, and the content of components above C25 in the produced oil decreased from 54.4% to 37%, indicating significant lightening of the crude oil. A field test was performed in a low-production huff and puff well. After treatment, the periodic oil production increased by 387 t, and the oil-to-gas ratio increased by 0.34, showing sound field application results. The study suggests that in-situ catalytic modification and viscosity reduction technology can induce irreversible viscosity reduction in crude oil, significantly lowering the viscosity of heavy oil and improving development efficiency, which can be further promoted and applied.