The purpose of this research is to investigate mechanisms that cause variations in the structure of hurricane eyewall. It has been shown from observations and numerical modeling studies that there are oscillations of the hurricane eyewall and are related to the hurricane intensity changes. The barotropic instability associated with the potential vorticity(PV) gradient around eyewall, which activates vortex Rossby waves and lateral mixing of potential vorticity, has been recognized as one viable process for causing the eyewall oscillations. Another process that is thought to contribute to lateral mixing is turbulence. This paper will focus on the relative roles of turbulence and the wave break down in determining fluctuation in eye and eyewall structure. Simulation results from a fine-mesh numerical model are used in this research. Several mesoscale models (MM5, WRF, ARPS) are adopted to examine the role of the horizontal momentum fluxes on eyewall variations. The relationship between the eyewall oscillations and hurricane intensity change are also investigated. Especially, the effects of grid scale and subgrid scale turbulence on these phenomena are preformed through set of simulations in which the diffusion and PBL scheme are altered. The numerical simulations are preformed for Hurricane Floyd (1999) because it was well simulated by most of the mesoscale models and was strong enough to have eyewall oscillation.