Characterization of a supersonic impinging jet in a laser cut kerf was conducted, with a Schlieren method, a total pressure measurement, and a CFD (Computational Fluid Dynamics) analysis to investigate gas dynamic effects of the jet in cutting processes. From the measurements, a flow field extension along a kerf direction inside the kerf, with higher feed pressure, smaller nozzle-workpiece distance, smaller kerf width, or lager nozzle diameter, was corresponding to the extension of the total pressure distribution at the kerf bottom. Also, with higher feed pressure, smaller nozzle-workpiece distance, wider kerf width, or lager nozzle diameter, positions of flow separation lines at both kerf side walls and a cutting front become deeper, and all values of total pressure distributions were increased. From the CFD results, it was shown that a nozzle jet was abruptly compressed forming a normal shock above the workpiece surface, and behind the shock the flow was expanded and accelerated downward and to a kerf direction. A flow separation and an associated recirculation zone occurring at the bottom of a cutting front were found. Imbalanced flow separations and recirculation zones at both side walls, and flickers of the flow inside the kerf were also observed. From the cutting experiments, it was found that better cutting performances were achievable with the conditions in which wider and deeper penetration of the flow field inside the kerf was obtainable.