To investigate the influence of high rotational speed swirl flow and rotational Reynolds number on sealing performance at high rotational speed, this paper presents a three-dimensional steady simulation of a rim seal model. The validity of the employed numerical method in computing cavity flow and sealing performance is verified through comparisons between experimental data and numerical calculations. On this foundation, the flow field distribution within the turbine cavity under varying conditions of swirl ratio and rotational Reynolds number is investigated. Furthermore, the variation in sealing efficiency is analyzed using the additional passive tracer method. The results reveal that changes in both the swirl ratio and the rotational Reynolds number exert significant impacts on the cavity flow field, thereby altering the sealing performance. Under conditions of constant cooling flow rate, increasing the cooling flow swirl ratio raises the total pressure in the cavity, resulting in an enhancement of the sealing efficiency at the high-radius locations of both the rotating and static walls. Specifically, as the swirl ratio increases from 0.36 to 1.08, the sealing efficiency of the static wall in the high-radius region increases by 6.3%. Under conditions of constant sealing clearance, increasing the rotational Reynolds number causes the vortex within the cavity to migrate towards the high-radius direction and the side of the rotating wall. When passing through the sealing clearance, the vortex entrains the gas, exacerbating the phenomenon of gas ingestion. As the rotational Reynolds number increases from 1.39×10⁶ to 4.87× 10⁶, the sealing efficiency first decreases and then increases with the sealing efficiency of the static wall in the high-radius region reaching only 0.42.