Scanning electrochemical microscopy (SECM) is an attractive technology to in-situ characterize the structural evolution and catalytic performance for various electrocatalysts. However, spatial and temporal resolution coupling are still the obstacles that limit its wide applications. Herein, a new operation mode, Fast Scan mode, was developed by improving the dual-pass scan mode, designing novel hardware structure, and employing thermal drift calibration software to achieve a high spatial and temporal resolution simultaneously. The temporal speed can achieve 4 Hz for a high spatial resolution (less than 30 nm) image. This operation mode was employed to dynamically track the phase transition process of molybdenum disulfide (MoS₂) over time and characterize the hydrogen evolution reaction (HER) catalytic activity on the edge of semiconducting MoS₂ quantitatively while minimizing the diffusional broadening effect and total amount of catalytic products generated above the surface. This new approach should be useful for in-situ tracking dynamic electrochemical processes, establishing the structure-activity relationship for structural complex electrocatalysts, and offering a strategy for high-speed scanning with other electrochemical imaging techniques.