The interaction of the fundamental and the subharmonic instability modes of an elliptic jet under excitations are investigated experimentally in this paper. Results indicated that the fundamental instability modef0saturated in the major axis location is almost the same as the subharmonic instability modef0/2 saturated in the minor axis. These two instability modes interact nonlinearly to produce the sum‐ and the difference‐modes. The newly produced instability modes grow and subsequently interact with other instability modes to produce other sum‐ and difference‐modes. A comb‐like spectrum resulted from the nonlinear interaction during the evolution process in the free shear layer of the elliptic jet flow.