The invention discloses a dynamic flash flood simulation method based on an irregular unstructured grid model. The simulation method comprises the following steps: selecting a simulation area, and collecting data; performing grid division aiming at a complex computational domain and an irregular terrain by adopting an irregular unstructured grid; describing water flow by adopting a two-dimensionalunsteady flow shallow water equations, and solving the equations by using a finite volume method and a Riemann approximate solver; calculating flood arrival time, flood inundation time, maximum floodinundation water depth, maximum flood level and maximum flood flow velocity of each grid unit; and obtaining flood arrival time isograms, flood inundation time isograms, maximum flood inundation water depth isograms, maximum flood level isograms and maximum flood flow velocity isograms. According to the method disclosed by the invention, dynamic simulation and simulation of flood inundation processes in flash flood susceptible areas based on the complex computational domain and the irregular terrain can be realized, the flood inundation range, inundation water depth, flow field and other flood elements are simulated and calculated in real time, and the visualized simulation of the flood inundation process is realized.