Abstract: Based on similarity principle, a water model with geometrical-similar ratio 1:7 is established to study circulation flow behavior of liquid in 145 t RH vacuum refining unit. The effect of lifting gas flowrate (60 〜140 m³/h), inserting depth of snorkel (400 ~ 600 mm) and liquid height in vacuum chamber (426 ~526 mm) on circulation flow rate and mixing time of liquid is researched. Results show that with increasing lifting gas flow-rate the circulation flow rate increases in approximate linear relation while the mixing time of liquid decreases in non-linear relation； the more ideal circulation flow rate of liquid is occurred with inserting depth of snorkel 500 mm and liquid height in vacuum chamber 526 mm ； with 130 m³/h lifting gas flow-rate, 600 mm inserting depth of snorkel and 526 mm liquid height in vacuum chamber the optimum liquid circulation flow characteristics are obtained.