Zinc-ion batteries (ZIBs) are promising energy storage devices due to their low cost, high safety, and high theoretical capacity. However, dendrite growth and chemical corrosion on the Zn anode limit their commercialization. This study introduces a fast and simple method using digital holographic microscopy (DHM) to monitor the electrode/electrolyte interface in situ, providing direct information on ion concentration evolution and predicting dendrite growth tendency. The effectiveness of this method is validated by the evaluation of thioacetamide (TAA) as an electrolyte additive. TAA is shown to regulate interfacial ion flux, induce dendrite-free Zn deposition, and construct adsorption layers to inhibit side reactions. DHM's advantages, including high temporal resolution, non-contact, and non-destructive operation, make it a promising approach for investigating the electrode/electrolyte interface in other battery systems. The study also demonstrates the enhanced electrochemical performance of Zn anodes in TAA-based electrolytes, confirmed by both DHM predictions and experimental results.Zinc-ion batteries (ZIBs) are promising energy storage devices due to their low cost, high safety, and high theoretical capacity. However, dendrite growth and chemical corrosion on the Zn anode limit their commercialization. This study introduces a fast and simple method using digital holographic microscopy (DHM) to monitor the electrode/electrolyte interface in situ, providing direct information on ion concentration evolution and predicting dendrite growth tendency. The effectiveness of this method is validated by the evaluation of thioacetamide (TAA) as an electrolyte additive. TAA is shown to regulate interfacial ion flux, induce dendrite-free Zn deposition, and construct adsorption layers to inhibit side reactions. DHM's advantages, including high temporal resolution, non-contact, and non-destructive operation, make it a promising approach for investigating the electrode/electrolyte interface in other battery systems. The study also demonstrates the enhanced electrochemical performance of Zn anodes in TAA-based electrolytes, confirmed by both DHM predictions and experimental results.