The effect of relative motion between the casing and turbine blade tip has been recognized as an important factor for tip aerothermal performance evaluation. Tight tip clearance is becoming one of the main objectives of engine manufacturers. This paper provides some insights on the topic that the impact of casing motion on the blade tip thermal performance could be different between nominal and tight tip clearances. A typical squealer tip geometry was employed, with coolant holes on the cavity floor near the pressure side rim. Three tip clearances, 1.1%, 0.6% and 0.2% of the span, are compared. The CFD method was validated against experimental data in the previous study. The results suggest that, in the tight tip situation, the effect of casing motion on cooling efficiency and flow structure is distinguished from the larger clearance situations. The scraping effect drives the leakage flow towards the blade suction surface, inducing high thermal load at tight clearance. The findings in this study highlight the importance of relative casing motion, especially at tight clearance.