Abstract: A three-dimensional numerical model that solves the Reynolds-averaged Navier–Stokes equations with the k-ε turbulence closure models based on COBRAS using a finite-volume method, has been adopted to investigate the effects of dam-break flow propagating through a laterally narrowed section. This model uses a pressure-implicit operators-splitting algorithm for pressure-velocity coupling and a volume-of-fluid method for free surface tracking. It was validated by previous laboratory experiments and numerical simulations were made for the dam-break flows in a flume with a narrowed section. The results show that high-intensity flow turbulences, negative waves and hydraulic jumps occurred upstream of the narrowed section. When a dam-break wave front reached the narrowed section, the free surface near its entrance suddenly rose and then waves were spreading gradually upstream and downstream. At the entrance of abrupt contraction, the dynamic pressure reached the maximum during flood peak formation and after that it was decreasing gradually, while the total pressure was able to maintain its relatively stable maximum in a certain time period around flood peak formation.