  The macroscopic-microscopic mass formula is further improved by considering
mirror nuclei constraint. The rms deviation with respect to 2149 measured
nuclear masses is reduced to 0.441 MeV. The shell corrections, the deformations
of nuclei, the neutron and proton drip lines, and the shell gaps are also
investigated to test the model. The rms deviation of alpha-decay energies of 46
super-heavy nuclei is reduced to 0.263 MeV. The central position of the
super-heavy island could lie around N=176~178 and Z=116~120 according to the
shell corrections of nuclei.
