  The symmetry energy coefficients for nuclei with mass number A=20~250 are
extracted from more than 2000 measured nuclear masses. With the semi-empirical
connection between the symmetry energy coefficients of finite nuclei and the
nuclear symmetry energy at reference densities, we investigate the density
dependence of symmetry energy of nuclear matter at subnormal densities. The
obtained results are compared with those extracted from other methods.
