<p>As one of the key components of compressed air energy storage systems (CAES), the performance of a closed centrifugal compressor is crucial to the overall system efficiency. To comprehend the internal flow characteristics and interaction mechanisms of various compressor parts, this paper employs a combination of numerical simulation and experimental research to investigate the sealing characteristics of the labyrinth seal on the wheel cover and how circumferential non-uniformities in the volute affect leakage in the wheel cover cavity of a closed centrifugal compressor used in compressed air energy storage. It is found that the labyrinth seal structure creates a pronounced anti-spin effect at the impeller inlet, significantly reducing cavity exit pressure and mixing losses, as well as decreasing cavity leakage mass flow rate. As the mass flow rate increases, the flow resistance increases, and the leakage rate drops. With the growth in pressure ratio, the inertial circulation force at the clearance of the labyrinth seal increases, and the relative leakage increases. In addition, the circumferential non-uniformity impact of the volute is conveyed along the path of the reverse pressure gradient to the upstream diffuser and wheel cover cavity. Under different flow regimes, the aerodynamic parameter distributions show variable response and lag effects throughout the circumference. The deviation of circumferential non-uniformity induced by variable rotating speed is significantly smaller than that produced by mass flow rate variation, and the non-uniformity of the flow field at low rotational speed is considerably weaker than that at high rotational speed.</p>