Abstract: In response to the problems of continuous drop of periodic oil production and oil-steam ratio in the intermediary and later stage of cyclic steam stimulation development of ultra-heavy oil in Block Shu-1 in Liaohe Oilfield, it is urgent to transfer to steam flooding as alternative technology. Therefore, it is necessary to determine the implementation boundary and conversion conditions for steam flooding technology. However, due to the complex underground conditions and unique fluidity of ultra-heavy oil, precise field-scale numerical simulations are difficult to conduct. To address this challenge, based on the scaled physical simulation experiments of steam flooding using two-dimension sand packed model, CMG-STARS modulus was utilized to establish a small-scale numerical model, followed by upgrading to field-scale pursuant to similarity criteria. An inverted nine-spot pattern(70 m injector-producer distance) numerical model was established. Systematic simulations were carried out on the implementation boundaries of steam flooding, including crude oil viscosity, reservoir permeability, oil layer thickness, and permeability variation coefficient, as well as conversion conditions, such as inter-well temperature, number of cyclic steam stimulation cycles, and reservoir pressure. The results show that the implementation boundaries for steam flooding in this block are: crude oil viscosity less than 300 Pa·s, reservoir permeability greater than 500×10⁻³ μm², permeability variation coefficient less than 0.5, and oil layer thickness less than 50 m. The optimal conversion conditions are: inter-well temperature reaching 85 ℃, after 14 cycles of steam huff and puff, and formation pressure at 3 MPa. These findings provide a theoretical basis for field trials and development plan optimization for converting cyclic steam stimulation to steam flooding for ultra-heavy oil of Block Shu-1.