The effect of structural flexibility on the maximum wave energy conversion by two interconnected floaters is investigated. For the wave energy converter (WEC), the relative pitch motion of two floaters is converted into electricity by a power take off (PTO) system, which is simplified as a linear damper. The hydrodynamic coefficients of the WEC are calculated based on linear potential flow theory. The coupled effects of structural deformation and hydrodynamic interaction are considered using an approximate approach based on discrete-modules and Euler-Bernoulli beam bending. Then equations of motion of the hinged two-floater WEC with structural deformation considered are established in frequency domain. Based on the motion equations, a mathematical model is proposed for evaluating the maximum wave energy conversion of a hinged two-floater WEC in waves. This mathematical model can be used to calculate the maximum power capture and the corresponding optimum PTO damping for both rigid and flexible two-floater WEC with or without motion constraints. Results show that the structural flexibility has a negative effect on the power capture performance for relatively large wave length but a positive influence for relatively small wave length. The motion constraints lead to a reduction of the captured power for both rigid and flexible WEC.