In this paper we study the decay estimates of fourth order Schrödinger operator H=Δ2+V(x) on R2 with a bounded decaying potential V(x). We first deduce asymptotic expansions resolvent H near zero threshold in presence resonances or eigenvalue, and then use them to establish L1−L∞ e−itH generated by H. Our methods used depend Littlewood-Paley decomposition oscillatory integral theory. Moreover, ...