Eyewall replacements occur in 70% of major tropical cyclones (TCs), and are associated with rapid changes in storm intensity and rapid broadening of strong winds. In this study, we present to use the radial gradient of absolute angular momentum with Holland’s wind profile as a simple diagnostic for eyewall replacement as internal variability of the storm. The diagnostic is solely dependent on the maximum wind speed, the radius of maximum wind, and the latitude and found to coincident with 70% of satellite observed concentric eyewalls for 1991-2020. The diagnostic can be expressed as a latitude-irrelevant Rossby Number of primary eyewall, varying with the peakedness of wind. It highlights the importance of pressure-wind relationship in eyewall replacement and provides a valuable tool to improve the understanding, modeling and risk assessment of storms with eyewall replacements.