A three-dimensional full-coupled mathematical model is established to study the fluid flow, heat transfer and solidification in a 450 mm × 350 mm × 90 mm beam-blank mold with two different types of submerged entry nozzle (SEN), namely single-port straight SEN and three-port radial flow SEN. Water modeling experiments, industrial trials and public results available in literature are performed to validate the numerical results. The results show that, with the straight SEN which has been widely applied in beam-blank continuous casting, there is a very inactive top free surface in the mold which level fluctuation magnitude is less than 1 mm and velocity magnitude is far from a reasonable interval, and the shell thickness distribution at the mold exit is very uneven, thick at the web but thin at the fillet. Moreover, there exists a “wavy contour” at the flange due to the washing effect of the off-center molten steel jet. While with the new designed radial flow SEN, a suitable meniscus status and a more uniform shell thickness at the mold exit can be obtained, which is helpful to avoid the breakouts caused by the rupture of thin fillet and the flange depression. The “self-braking” effect caused by two radial flow SENs provides good flow stability at the web center.