Surface plasmon resonances of optical bowtie nanoantennas with symmetry breaking are studied numerically using the finite-element method. Beginning with both x-axial and y-axial symmetry, bowtie structures are reshaped by varying two parameters (edge lengths and bow angles) to create various symmetries to achieve controllable resonant modes and gap enhancement in the visible and infrared wavelength range. The four edges’ coupling is the main factor contributing to the final fundamental resonances. Double fundamental resonances can be achieved in bowtie structures with x-axial or y-axial symmetry. These properties can guide both the engineering and the fabrication of plasmonic nanoantennas.