Inkjet technology being an essential tool features high resolution and wide applicability. The generation of stable droplets is of great significance in many applications including 3D printing, solar cells and drug delivery. A stable ejected droplet can be a single droplet without satellite droplets (Situation 1), or a single primary droplet with a satellite that merges into the primary later (Situation 2). The deformation process of a stable droplet is directly related to accuracy and efficiency of the droplet delivery. In this paper, we adopt computational fluid dynamics to investigate deformation of a moving stable micro-droplet. It is found that as the driving force rises, the ejected droplets change from Situation 1 to Situation 2, and then to the unstable state after the driving force exceeds a critical value. In the meantime, the maximum deformation of the droplet firstly increases, and then decreases followed by a further increase. The minimum deformation undergoes a converse transition. It further reveals that two essential points of the maximum deformation curves, the peak point (within Situation 1) and the transition point (from Situation 1 to Situation 2), are correlated with ratio of the droplet velocity to the Capillary velocity. The peak point has a ratio between 2.7 and 3.1, and the transition point locates where the ratio plus a constant equals 3.4. New control methods have proposed based on the locations of the maximum deformation extent.