Recent studies have demonstrated that the turbine blade with a squealer tip has less aerodynamic loss than that with a flat tip. However, there exists an area of high heat transfer coefficient (HTC) in the frontal region of the cavity floor. The present study focuses on the effect of squealer rim slot structure on turbine blade aerothermal performance. An experiment of transient thermal measurement is carried out for a non-slot squealer tip to validate the numerical setup and the choice of turbulence model. ANSYS CFX is utilized to conduct the numerical simulations of cases with and without slot structure and they are both validated by the experimental data. Through the experimental and CFD results, it can be found that the case with a slot on the pressure side of the squealer rim has smaller area of high HTC region and the aerodynamic efficiency is raised. Moreover, the effect of different sizes of the slot is investigated numerically and it also has a great impact on the heat transfer and aerodynamics. The quantity of the flow passing through the slot can largely influence the flow field of the tip gap and the cavity. Thus, the heat transfer of these areas and the aerodynamic efficiency of the blade vary from the slot size.