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This paper describes a numerical study on the H2/N2 jet diffusion flame interacted with large scale vortices generated by oscillating the fuel velocity. Computations are made of transient diffusion flames. Attentions are paid to the dynamic behavior of the diffusion flames with the transient local extinction and to the flame structure in relation to the local flame parameters such as local flame stretch and preferential diffusion. The obtained results are as follows. (1) When the amplitude of fuel velocity is relatively small, flame extinction does not occur by interaction between flame and vortex, and the temperature characteristics depends on the effect of the preferential diffusion among species and the non-unity Lewis number effect. (2) When the amplitude of fuel velocity is large, the temperature decreases in the region where the stretch rate near the circumferential part of vortex is high. According to the procedure of non-equilibrium of chemical reaction, temperature and heat release rate begins to decrease at the region and the effect results in flame extinction. (3) The position of the local flame extinction does not always agree with that of higher stretch rate. During the procedure of the flame extinction, the position of higher stretch rate moves downstream from the position of extinction. (4) One of the edge flames constructed at the extinction propagates along the stoichiometric line around the vortex to the upstream region, and it is again connected with another edge flame.