A sequential designed process was utilized to deposit Pt atoms with different compositions on the surface of Ru nanoparticles through Polyol reaction. In this research work, we successfully synthesized Ru/Pt nanocrystallites in core-shell structures with mole ratios from 10:1 to 10:30. The transition of crystal structure in bimetal nanocrystals (BiNCs), as a function of the Ru/Pt ratio, was elucidated by XRD characterization. With the combined results on the fitting of X-ray absorption spectra and the TEM micrographs of samples, the transition of local structures were quantitatively characterized. The data show those transitions of local structure is induced by the interface stress when there exists a difference in dimension between core-shell components of the particle. The stress induced core-shell inversion can be demonstrated in the following scheme.