  We study steady Boltzmann equation in half-space, which arises in the Knudsen
boundary layer problem, with diffusive reflection boundary conditions. Under
certain admissible conditions and the source term decaying exponentially, we
establish the existence of boundary layer solution for both linear and
nonlinear Boltzmann equation in half-space with diffusive reflection boundary
condition in $L^\infty_{x,v}$ when the far-field Mach number of the Maxwellian
is zero. The continuity and the spacial decay of the solution are obtained. The
uniqueness is established under some constraint conditions.
