Abstract: A fluid model is developed in magnetized electronegative plasma sheath with two species of positive ions.It is shown that one-dimensional stationary plasma sheath is affected by ions-neutral collisions.The range of ion Mach numbers depends on density ratio of Ar⁺ to He⁺ and collision parameter. Collision efkct on charge density in the sheath is obvious as density of negative ions is small. Density of electron and negative ion decreases quickly.Two kinds of positive ion density present different fluctuations.Collision effect on ion velocitv distribution in the sheath is obvious as density of negative ions is great. In addition,collision paramcte affects density distribution of charge particles clearly as density ratio of two species of positive ions is great.

Key words: plasma, magnetic sheath, collision, Bohm criterion