Abstract: An efficient aeroelastic computational model is proposed by coupling reduced unsteady vortex lattice method with structural equations of motion. A tight coupling between aerodynamic and structural equations is fulfilled by the introduction of pseudo-time iteration. A model reducing is carried out by proper orthogonal decomposition (POD) technique. This method is validated by the aeroelastic computation on a plunging foil with spanwise flexibility. The results show that the full model of the vortex lattice method can be well approximated by the superposition of only first 7 POD modes. The computational speed of the current problem can be significantly increased (about 10 times) with very little accuracy loss (about 1%). Moreover, in the current validation test, the method performs equally well both inside and outside the parameter variation range of samples for the POD analysis.