Effect of the initially atom coherence on the two-mode-entanglement of three-level atom in cascade configuration was studied, according to the entanglement criterion proposed by Duan et al. The result shows that, entanglemengt of two-mode cavity field can be induced only when the atom coherence exists. If gain coefficient is unchanged, the degree of entanglement firstly increases and then decreases with the increase of detuning. In certain detuning circumstances, the degree of entanglement of two-mode cavity field increases with the increase of gain coefficient. If detuning is zero, the entanglemengt of two-mode cavity field can’t be created, no matter whether the atomic coherence exists or not.