This paper investigates the thermal performance of cavity tips in a transonic high pressure turbine cascade. Numerical methods were first validated and then used to study more cases. The flow physics within the tip gap and the distribution of Nusselt number on the blade tip were presented. The effects of relative motion between the blade tip and the endwall were studied. For both cases with a stationary endwall or a moving endwall, a cavity vortex appears within the tip cavity. It is found that a cavity scraping vortex forms within the tip cavity as the endwall moves relatively to the blade tip, which was not observed before. The effects of the cavity scraping vortex on the distribution of Nusselt number are explained. Then, the effects of the squealer width and height on the thermal performance of the cavity tip were investigated. The flow physics within the tip cavity varies as the squealer geometry changes. As a result, the thermal performance of the cavity tips is different. The results show that increasing the height of the squealer reduces the average Nusselt number on the blade tip. The average Nusselt number and the heat flux on different parts of the blade tip, and the thermal performance of the blade surface near tip region and the loss of different blade tips are also discussed in this paper. (C) 2015 Elsevier Ltd. All rights reserved.