To improve the resolution accuracy and get deep insight into the flow structures in squealer tip gap, the Very Large Eddy Simulation (VLES) method was implemented into the commercial CFD (Computational Fluid Dynamics) solver with the User Defined Function (UDF). Based on the published experimental data, the numerical accuracy of VLES method was validated. With VLES method, the unsteady heat transfer coefficient distributions on the squealer tip and total pressure loss in the blade passage were computed. The influences of coherent vortex structures on aero-thermal performance in the squealer tip gap were analyzed. The results show that the Brown-Roshko vortices are the main driver for the formation of cavity vortex system. The direct impingement of pass-over leakage into the cavity is the main cause of high heat transfer area on the cavity floor near leading edge. The unsteady fluctuations of leakage rate through the tip gap reach about ±8% of the time-averaged value. The development of leakage vortex accounts for the major contribution of total pressure loss in the squealer tipped blade. Due to flow unsteadiness, the fluctuation of pitch-averaged total pressure loss coefficient induced by leakage vortex system reaches about ±30% of the time-averaged value. The unsteady fluctuation of pitch-averaged heat transfer coefficient on the cavity floor reaches about ±35% of the time-averaged value, while on the shroud surface it is only fluctuated by about ±10%.