In this paper, the atomic vibration modes of Si(lll) planar strcture with different layers have been calculated using the dynamic matrix method. The Raman frenquency shift, which moves to lower wave number greatly for microcrystals compared with single crystals, can be explained by the activation of surface modes. By hybridized orbical theroy, the change of surface force constants was obtained. The calculated frequency of surface modes, 469cm-1, is close to the experimental result 430 cm-1 first reported by Okada.