  The site-random Ising spin glass model is investigated. We find a rigorous
symmetry for the SG correlation and the free energy, which provides some
restrictions in the phase diagram. Using the defect energies calculated by the
numerical transfer matrix method, we obtain evidence for the existence of the
SG phase in the two-dimensional Ising system. We suggest that the transitions
from the FM and the AF phases in the ground state in this model can be
explained by the percolated-cluster picture, which is quite different from the
frustration picture in the conventional $\pm J$ model.
