Attachment probabilities of an inclusion on a bubble in the molten steel both under laminar condition and under turbulent condition were discussed. Collision probability, interception collision probability, inertial collision probability, and adhesion probability were formulated under laminar condition. A simple mathematical model of inclusion removal by bubble flotation under laminar condition was developed, and the effects of gas flowrate, bubble size, and time on inclusion were discussed. A numerical model was developed to calculate attachment probabilities of an inclusion on a bubble under turbulent conditions. The steady turbulent flow of the molten steel around bubbles was calculated for the fixed turbulent kinetic energy firstly. Then, the interaction between inclusions and bubbles was studied by injecting inclusions into the fluid flow. Finally, the attachment probability was calculated for different bubble sizes and inclusion sizes under different turbulent conditions.