<p>In the continuous casting of ultra-thick slabs, the flow and solidification within the mold are significantly influenced by the structural parameters of the submerged entry nozzle (SEN). Using a coupled solidification-flow model, a four-hole SEN with asymmetric outlet angles was designed for ultra-thick slab casting, leading to reduced broad-face shell thinning and improved end solidification uniformity. The effects of different port area, port angle, and casting speeds on the flow and solidification uniformity were systematically analyzed. The results showed that, compared with two-port SEN, the four-port SEN reduces the thickness of the shell at the center of the broad surface under the impact of the steel flow stream towards the broad surface. With fixed narrow-face side port parameters, increasing both the area and angle of the broad face ports can effectively mitigate non-uniform of the solidification end. When port area exceeds 3000 mm² or angle exceeds 20 deg, the broad face shell at the mold exit is reduced significantly, and the strain concentration would raise the risk of slab crack. The optimized structure of four-port asymmetric angled SEN based on shell safety and uniform solidification for cross section 450 mm × 2070 mm are: area ≤ 3000 mm², angle ≤ 20 deg, which can reduce the non-uniform solidification length from 1.92 to 0.87&#xa0;m. An increase in casting speed intensifies both the degree of non-uniform solidification and the maximum strain at the broad face center. Within the casting speed range of 0.40 to 0.50 m/min, the maximum strain at the broad face is 0.016, indicating no risk of crack. This work proposes a dual-criterion SEN design approach based on shell safety and degree of non-uniform solidification, which provides references for controlling solidification quality in continuous casting of ultra-thick slabs.</p>