Lithium metal batteries are considered the holy grail for next-generation high-energy systems. However, lithium anode faces poor reversibility, unsatisfying cyclability and rate capability due to its uncontrollable plating/stripping behavior. While galvanostatic conditions are extensively studied, the behavior under more realistic application scenarios with variable inputs are less explored. Here, an in situ imaging platform using in-plane microdevice configurations is developed to effectively investigate Li plating/stripping behavior under dynamic conditions. This platform offers high detectivity for analyzing the nuclei size, density, distribution, and growth location, rate, and mode. It is for the first time revealed that nuclei density and growth locations remain constant and are solely determined by the initial nucleation overpotentials during dynamic plating. A transition in growth modes from uniform granular growth to tip-induced dendrite growth, and finally to directional growth among the dendrites is also observed. Guided by these findings, a dynamic plating protocol is proposed, which can greatly improve the Li reversibility and cycling stability. This work not only provides a novel approach to visualize the evolution of key nucleation and growth parameters, especially under variable inputs, but also offers valuable guidance for the future industrialization of metal batteries and the rational design of charging facilities.