Information of avalanche size distribution is measured by calculating information entropy (IE) in the Bak-Sneppen evolution model. It is found that the IE increases as the model evolves. Specifically, we establish the relation between the IE and the self-organized threshold fc. The variation of the IE near the critical point yields an exponent entropy index E = (т - l)/<б, where т and б represent the critical exponents for avalanche size distribution and avalanche size cutoff, respectively. A new quantity Dт(g) (g = 1 - (fc - G)(r-1)/б , where G is the gap of the current state), denned as 1 - Ⅰт(g)/Ⅰт(l), with Ⅰт(g) and Ⅰт(l) being the IE for the current state and the critical one respectively, is suggested that it represents the distance between the state with gap G and the critical one.