In modern gas turbines, turbine blade tips often face severe thermal erosion and aerodynamic losses. Squealer cavity structures have demonstrated significant advantages in improving tip harsh working conditions, making them a widely researched and applied solution. Among them, the squealer tip with rail crown holes has been proved a novel and more effective structure for controlling tip leakage flow and enhancing tip cooling. In this paper, for the novel structure, the effects of tip gaps and cavity depths on its performance are investigated. The results show that, as the gap size increases, more gap leakage flow impinges on the leading-edge floor, and the swirling strength of the cavity vortex is enhanced, which causes the increasing heat transfer coefficient (h) and decreasing film cooling efficiency (η) on the cavity floor. The coolant is distributed over a larger radial space up the rail with the increasing gap size, thereby the cooling intensity on the rail crown is diminished. In the case with a smaller gap, the impact of coolant on the leakage flow rate is more pronounced, and the leakage flow exhibits a distinct stripe-like morphology. When the cavity depth alters, the η distribution on the rail crown surface remains unchanged, thereby it primarily correlates with the gap size. In the small cavity depth scheme, the pass-over coolant is subjected to axial shear by the cavity flow within the cavity. Consequently, the lower part of the coolant flow is scraped along the axial direction by the cavity flow, resulting in the coolant jets having a significantly dispersed flow state but with strong swirling characteristics. As the cavity depth increases, the scraping effect on the coolant is reduced, thereby the coolant can maintain its original form as it flows to the suction side, thereby forming localized high-h regions in a spotted pattern on the suction-side rail crown.