  In this paper, one new integrable modified extended Toda hierarchy(METH) is
constructed with the help of two logarithmic Lax operators. With this
modification, the interpolated spatial flow is added to make all flows
complete. To show more integrable properties of the METH, the bi-Hamiltonian
structure and tau symmetry of the METH will be given. The additional symmetry
flows of this new hierarchy are presented. These flows form an infinite
dimensional Lie algebra of Block type.
