A nano-antenna with two resonant frequencies and wider resonant areas was constructed. On the basis of the finite integral method , the resonant properties of the surface plasmon optical nano-antenna constructed by Au were calculated and the resonant frequencies and resonant fields in resonant areas were mainly simulated. The experiments show that there are two resonant areas in different resonant frequencies, which are 270 THz at the middle gap and 390 THz at the side gap. Their resonant electric fields are up to 700 V/m, which is about 18 times higher than that of the common dipole antenna when the excitation field is 1 V/m. The resonance field at the first resonant area is confined at the central part from 10 nm to 25 nm along the Z-axis direction, the resonant frequency is almost not changed and the magnitude is greater. The structure with a glass substrate of refraction index of 1.5 is also considered, the resonant field is up to 800 V/m, whereas the resonant center frequencies are almost not changed. The proposed structure has potential applications to high-quality optical antennas, solar cells, and biosensors.