Drilling is dated back to early civilization and with industrial development, it becomes an important technology. The term drilling refers to the penetration in stone for making hole in the ground strata. One of the problems for earth dam, drilling, road construction is to control the seepage. In the construction of dams, particularly in earth dams, the water proof walls are used to control the seepage. The waterproof walls are usually made of bentonite mixture and have been implemented as discrete panels. In rotary drilling pile, bentonite mixture (water and clay) and paste cement (drilling fluid) prevents the loss of concrete during the casting. Bentonite can also act as a medium to cool the drilling tip and to help lubricating the rotary motion. The performance of bentonite in drillings is affected by rheological properties and resistance behavior of bentonite fluid flow in the cavity of ground strata. In other word, the workability and flow ability of bentonite have a direct relation with the rheological properties. In accordance with guidelines API-13A, the drilling fluids must be used after 24 hours and the percentage of solids bentonite in water should be about 3-10. The marsh funnel test is used to measure the workability and flow ability of bentonite. Depending to the type of ground strata and construction consideration, the discharge time of specific volume of fluid in the marsh funnel is used to determine the viscosity of fluid. Various mathematical models represent the rheological behavior of Non-Newtonian fluid such as bentonite. Some of these models are Bingham, Herschel-Bulkley, and Casson. In this investigation, the effect of hydration time on the rheological properties of bentonite is studied. Samples 5, 7 and 10 percent of the bentonite are made. Rheological properties including the yield stress and viscosity of the samples are measured with Viscometer model HAKKE RV12. The comparison of rheological properties of bentonite samples shows that over the time, the yield stress increases first and then reduces. The viscosity almost remains constant over the time. The dam break problem test is performed for samples of bentonite and past cement. Flow profile of fluid during dam break test is obtained by image processing (in Matlab Software). The flow regimes (Laminar or Turbulent flow) of dam break problem were also examined. Numerical simulations of dam break problem are done by SPH method (Mesh free and Lagrangian method) and verified with experimental data. The results show that numerical simulations of turbulent and laminar flow are similar and both models are consistent with experimental results, which show that the SPH method is an appropriate method for simulation of large deformation and free surface problem. In the simulation, the fluid is considered as a homogenous fluid and Casson model are adopted as the rhelogical model. Finally, two cases of 2-D numerical simulation of water flow in the marsh funnel test are presented. The results of simulation of discharge time in the marsh funnel test results are similar to analytical results. Key Words: Drilling, Bentonite fluids, Rheology, Marsh funnel Viscometer, Dam break, Non-Newtonian fluid, SPH method