The equilibrium geometrical structures of ground state of small Yn(n＝2—8) clusters are optimized by mean of density functional theory(DFT), and the ionization potentials are calculated. The results show that the most stable structures of clusters tend to maximize the average coordination number of Y atoms. The value of ionization potential shows uo magic number or odd-even alternations, this would imply that the threshold for photoionization occurs mainly from a localized 4d orbital rather than from a 5s orbital of Y clusters. It is the first time to come up with a modification of the analytical formula of calculating ionization potential of Y clusters proposed by Tomasz, and the new analytical formula is in better agreement with experiment.