An investigation of the gamma' formation and its morphology evolution in the bulk undercooled DD3 single crystal superalloy is performed. The application of a molten salt denucleating technique combined with thermal cycle enables such investigation over a wide range of undercooling up to 210 K. The microstructure formation has been respectively discussed with respect to undercooling, nucleation and solute segregation during solidification and post-solidification, by employing the classical nucleation theory. Furthermore, TEM and SEM technique are adopted to reveal the gamma' microscopy and to illustrate other factors correlated to the gamma' precipitation. It is found that the size, fraction, and distribution of precipitated gamma' in as-solidified DD3 single crystal superalloy are all influenced by melt undercooling.