In order to raise the efficiency of the filling process of milk into 1,000-mL gable-top cartons, the effect of filling operation conditions on flow dynamics of milk were computationally considered using the Volume-of-Fluid (VOF) method. In the numerical simulation, the shear-thinning property of milk was modeled with the Carreau-Yasuda model, and the effects of the lifting operation of the gable top carton and filling speed (the number of milk cartons filled per hour) on the flow dynamics of the milk were examined. It was shown by computation that, without the lifting operation, milk that struck the bottom of the carton largely splashed up and out the carton. The lifting of the carton reduces the height of the splash. To examine the effect of the filling speed, one faster and one slower speed than the standard (current empirically selected) operating speed were considered. It was found that the standard speed is appropriate for the present production process.