This work is aimed at designing an optical nano-antenna structure to enhance the optical absorption in 1.0−1.7 μm and improve the performance of InP-based InGaAs sensors. We report comprehensive analysis of an optical nano-antenna structure of metallic ball array for surface plasmon enhancement of near-infrared photodetection. The enhancement capability of metallic ball array on InP substrate with periodicity in the range of 600−1200 nm and diameters in the range 100−300nm has been studied by theoretical modeling with a finite-difference time-domain(FDTD) method. Our simulation results show that the highest transmission efficiency is achieved when the diameter of the ball is around and the optimized periodicity of the ball array is around 800nm. After comparing the transmission spectra of the arrays made of different metals, silver is found to be the best. Because of the speciality of SPP modes, the enhancement relative to wavelengths near 1.1μm is obviously weaker than that near longer wavelengths. Coating a SiO<sub>2</sub> film about 500nm over the arrays is found to be an effective solution to achieve higher transmission efficiency around 1.1μm.