We study the nonreciprocal Tamm plasmon polaritons (TPPs) inside the light cone, which can be directly excited at the interface between the one-dimensional photonic crystal (1DPC) and magneto-optical (MO) metal film. Applying an external magnetic field on the MO metal, the broken time-reversal symmetry gives rise to such nonreciprocal electrons oscillation mediated plasmon mode. Separately exciting the forward and backward TPPs, light can be transmitted and reflected in one-way. An analytic dispersion relation based on admittance-matching approach is obtained. This design offers promising potential in realizing the optical diode.