Catalysis is a kinetics behavior, and developing the kinetics-assisted discrimination of the active sites is an important yet challenging issue in the heterogeneous catalysis. Herein, we combine the multifaceted kinetics analysis with the model calculations to discriminate the dominant active sites in Pd-catalyzed semihydrogenation of acetylene. The size-insensitive activation energy of >= 3.1 nm sized Pd catalysts with similar electronic properties suggests that only one typed active site mainly dominates the acetylene hydrogenation. The results of model calculations, based on the specific cuboctahedron shape of Pd nanoparticles on CNT, indicate that the Pd(111) facet is dominant active sites for the reaction and the formation of C-4 byproduct, while the Pd corner site for the formation of ethane. Moreover, for the Pd particle size being smaller than 3.1 nm, the catalysts exhibit higher activation energy but higher TOF, due to their lower Pd-0 3d binding energy and higher pre-exponential factor, respectively.