The property free of dendrite enables magnesium a potential candidate for next generation rechargeable metal anode battery. However, due to limited understanding on interfacial transportation of magnesium, stagnant progress is made in terms of high surface impedance, compatible cathode material and etc. Herein, we systematically examine the relationship between current density and magnesium deposition in diffusion-limited region by introducing the concept of over-limiting current. To evaluate, we develop a set of method to regulate the morphology of the magnesium and propose a possible scheme of magnesium deposition mechanism which is proved by Sand’s formula and the result of in-situ observation. Most interestingly, a dendritic morphology of magnesium deposition is detected for first time during observation.