Isolated-core excitation and autoionization detection method are combined to measure even-parity high-lying excited states of Sm atom. The experimental results are classified and discussed in detail in the light of different autoionization channels. With the information of energy levels and their relative intensities converging to different thresholds, the Rydberg states are identified from the valence states in the same region. In addition, with the effective technique to recognise different types of high-lying states, the spectroscopic properties of Rydberg states and valence states in the region between 41800 cm-1 and 43800 cm-1 are discussed and analyzed in detail.