This study proposes a new-fashioned plasmonic photoconductive antenna (PCA) with high optical-to-terahertz (THz) conversion efficiency. Finite element method was used to investigate and optimize the interaction of 800 nm femtosecond laser with the designed nanodisk array in the antenna's gap using its geometrical parameters. According to the simulation results, our optimized nanoplasmonic structure showed more than 38% enhancement in the absorption efficiency compared to the conventional structure without any nanostructure. Measuring the THz radiation of the fabricated PCAs using a time domain spectroscopy setup exhibited an exceptional 5.6 times higher electric field in 0.1–2.5 THz range compared to a similar PCA but without nanoplasmonic structure.