Abstarct: Spillway are designed to pass high discharges on the hydraulic structures No damage to structure and It is not entered around. In recent decades, stepped spillways as a suitable solution for energy dissipation Special attention has been placed. Stepped consists the steps that are located near the crest began to toe continued in downstream. Although energy dissipation above stepped spillways, in downstream some energy dissipation not remain that it is caused bed erosion and create hole on it. By studying the phenomenon of scour downstream of the stepped spillway, effective parameters the phenomenon, discharge Flow on the unit width (q), height Falling (H), tailwater depth (y_t), the average diameter material (d_50), have been recognized as contributing factors and the dimensionaless parameter is obtained by using dimensional analysis, which tests needed on the relationship between the planned have. These experiments were done for materials with uniform grain size, experiment with four diameters 0/3, 1, 3/5, 6/8 Millimeter and 7 discharge 2/5, 5/5, 7/5, 9/5, 11/5, 13/5, 16 and tailwater depth was different. In these experiments, the parameters of the maximum scour depth tailwater surface (d_s), distance and location of the maximum scour depth of spillway (L_c), were measured. The results show that with the increase (d_50) in the same hydraulic conditions, the maximum scour depth decreases. With increasing depth downstream (y_t), the maximum scour depth decreases. The effect of two parameters (d_50) and (y_t) both observed that scour dimensions are considerably reduced.