  The compact dark objects with very large masses residing at the centres of
galaxies are believed to be black holes. Due to the gravitational lensing
effect, they would cast a shadow larger than their horizon size over the
background, whose shape and size can be calculated. For the supermassive black
hole candidate Sgr A*, this shadow spans an angular size of about 50 micro arc
second, which is under the resolution attainable with the current astronomical
instruments. Such a shadow image of Sgr A* will be observable at about 1 mm
wavelength, considering the scatter broadening by the interstellar medium. By
simulating the black hole shadow image of Sgr A* with the radiatively
inefficient accretion flow model, we demonstrate that analyzing the properties
of the visibility function can help us determine some parameters of the black
hole configuration, which is instructive to the sub-millimeter VLBI
observations of Sgr A* in the near future.
