In hydrodynamic and hydraulic science, free surface flows are important but they are difficult to simulate because boundary conditions are required on an arbitrarily moving surface. Smoothed particle hydrodynamics (SPH) is a meshfree, Lagrangian particle method for modeling free surface flows such as dam break. One of problems in SPH is time consuming calculations in cases that they occurrence time are large. They need computers with strong CPU and memory. Recently, the parallel is used in this situation. In this paper, the influence of time scale in free surface flow simulation using SPH is considered. Dam break simulation with SPH in different scales is investigated and time scale influence is then obtained. For SPH model verification, the results were compared with experimental and numerical results of pervious researches. The dam break results as free surface flow show that the model with less scale model has less time of occurrence. Thus, the computer run time was decreased. The relation between two scales in dam break simulation indicates that the Froude law for free surface flow is valid. For models with scales of 3 and 6 with equal number of particles, the time of occurrence and computation were decreased about 42% and 59%, respectively. Therefore the computers run time can be decreased when this new-proposed scheme isused.