Slot coating is one of the frequently used coating processes in display and battery industry due to the high accuracy, fast production rate and cost effectiveness. An important issue is the prediction of coating stability that is difficult due to lack of reliable theoretical models. A frequently used model is viscocapillary model that evaluates the coating stability using a force balance between surface tension and viscous force. Although the model provides good physical insight, its predictions are inaccurate for large capillary number flows because it doesn’t consider the inertia of the ink flow. Thus, we propose an improved viscocapillary model which accounts for inertia effects in the coating bead. We found that the model predictions are in good agreement with numerical results on the ink flow of slot coating for a wide range capillary number.