In this study the scour mechanism and the effect of some of the important parameters such as jet velocities, impinging jet distance from the upstream wall and tailwater depth on the longitudinal scour profile due to 3d simoultaneous wall and impinging jet are investigated experimentally. Experiments were conducted in a channel 10 m long, 1 m height and 0.57 m width. For generating jet flow, two pipes with 1 cm inside diameter and 2 m long were used. Uniform sediment with median size of 1.05 mm was used as the bed material. The experiments showed that the jet distances, jet velocities and tailwater depth have significant effect on scour hole profile. Depending on the jet velocities, tailwater depth and the distance of the impinging jet from the upstream wall, two types of longitudinal scour profiles are observed.