  We analyze the AdS_3 x M_7 type supersymmetric solutions, including
non-trivial fluxes, of the Killing spinor equations in the heterotic
supergravity. We classify these solutions by their G-structures and intrinsic
torsions, for the cases that the number of seven-dimensional Killing spinors N
are equal to 1,2,3 and 4. We find that the solutions cannot have non-trivial
warp factor and the seven dimensional manifold M_7 is charactrized by
G_2(SU(3))-structures for N=1 (2) case and SU(2)-structure for N=3 and 4 cases.
They are further classified by their non-trivial intrinsic torsions. It is
shown, including the leading order \alpha'-corrections, that if we impose the
Bianchi identities, the integrability conditions of the Killing spinor
equations imply all the field equations.
