Abstract A new concept of point-absorber wave energy converter (WEC) with a waterproof outer-floater and a built-in power take-off (BI-PTO) mechanism, named Dual-Resonance WEC (DR-WEC), is put forward and investigated by experiments and numerical simulations. The BI-PTO mechanism includes spring, sliding-mass and damping systems, where the spring system is the most complicated and should be designed specially. A 1:10 scale model is designed. The mechanical performance of the BI-PTO system is investigated by a bench test. The results have shown that the design is feasible, and the added inertia effect of the BI-PTO has a negative influence on the power output. The average mechanical efficiency of the BI-PTO is 65.8% with maximum up to 80.0%. The motion and power responses of the DR-WEC are studied by a wave tank experiment and a linear numerical model with corrected mechanical added mass and viscosity. The viscous added mass and damping correction coefficients are obtained by a free decay test. The good agreement between the experimental measurements and numerical simulations has indicated that the present numerical model with corrections is of enough accuracy and the effects of mooring system and other degree of freedoms on the heave motion and power responses can be ignored.