Flooding caused by dam failure is been one of the most awful events in the past two centuries. In this type of flooding, a considerable amount of water releases in the river downstream in a short time and causes huge waves in the coastal. Due to the nature of wave, the use of mathematical models is common for simulating advancing and spreading of flood caused by it. In this case study, the subsequences of the flood volume released by the failure of Mirza Shirazi  storage dam that is under construction (in Fars province) and estimating of damage with respect to two probable dam break scenarios: 1) immediate failure due to overtopping; and 2) gradual failure due to overtopping, is been investigated. In immediate failure scenario, calculated peak of flood discharge at the point of failure was 118,000 m3/s and in gradual failure was 80,000 m3/s. The average velocity of water in the river bed in immediate failure scenario is 10.2 m/s and in gradual failure scenario is 5.06 m/s. The result estimated damage cost of flood caused by dam break, in scenario of gradual failure is 5578 billion Rials and in immediate scenario is 9136 billion Rials.