Using the one-atom theory (OA), the atomic state of Pt-electrocatalyst with fcc structure was determined as follows: [Xe] (5dn)6.48 (5dc)2.02 (6Sc)1.48(6sf)0.02. The atomic states of this metal with hcp and bcc structures of primary characteristic crystals and liquid state was also studied. According to its atomic states, the relationship between the atomic states and crystalline structure, catalytic performance and conductivity was explained qualitatively. The potential curve, the temperature dependence of bulk modulus and linear thermal expansion coefficient of fcc-Pt were calculated quantitatively.