<p>High-speed continuous casting is an important approach for enterprises to improve production efficiency, reduce costs, and achieve energy conservation and emission reduction. However, elevated casting speeds tend to induce frequent slag entrapment and deteriorate slab quality. Consequently, elucidating the mechanisms underlying slag entrapment under high casting speed conditions and devising effective control strategies are of critical importance. In this study, a hydraulic model satisfying equality with the prototype in both Froude number and Weber number was established, and a numerical calculation model coupling large eddy simulation and the volume of fluid method was developed, successfully reproducing the entire process of slag entrapment. Systematic revelation of the slag entrapment mechanism at high casting speeds was achieved, and a novel submerged entry nozzle (N-SEN) was developed. The results indicated that at casting speeds of 2.0, 2.2, and 2.4 m/min, the N-SEN reduced the maximum meniscus flow velocity by 33.1, 42.5, and 44.7 pct, respectively, and decreased the velocity difference at different meniscus positions from 0.071, 0.092, and 0.115 m/s to 0.024, 0.025, and 0.03 m/s. Furthermore, the non-uniform turbulent flow phenomenon of the side-port jet was eliminated, and the slag entrapment frequency was reduced. Specifically, the average first-order differential standard deviation of the side-port flow rate decreased from 0.185, 0.244, and 0.288 to 0.0030, 0.0039, and 0.0050. At a casting speed of 2.4 m/min, the amount of entrapped slag decreased by 45.97 pct. The clarification of the slag entrapment mechanism and the introduction of N-SEN in this study provide theoretical support and technical reference for producing high-quality slabs in high-speed continuous casting.</p>