There are many parameters that influence droplet ejection performance, i.e. printing quality, of inkjet print head such as ejection velocity and directionality of ink droplet. Ink droplet with larger ejection velocity from an inkjet print head nozzle exit will be less affected by the surrounded air disturbance and keep a good directionality. The printing quality of a thermal bubble inkjet print head is also affected by bubble growth dynamics. It depends on the proper geometry and size designs of micro-fluidic ink channel within the inkjet print head such as nozzle orifice, ink firing chamber and heaters. This work used computational fluid dynamics (CFD) method to study the parameters and effects on droplet ejection performance of thermal bubble inkjet print head for both top and back shooting type of thermal bubble nucleation. The numerical scheme, volume of fluid (VOF) method, has been used to deal with the interface between surrounded air and droplet liquid.