A silicon photonic crystal nanobeam caivity based on deep- etching method is presented. Using finite difference time domain (FDTD) method, the influence of deep- etching on the Q factor of nanobeam cavities is designed and analyzed. The calculated results show that the deep- etching scheme can keep the high-Q value close to the air-bridge peer, as well as robust mechanical strength. The devices are fabricated on silicon on insulator (SOI) platform using electron beam lithography (EBL) and inductively coupled plasma (ICP). Scanning electron microscope (SEM) and atomic force microscope (AFM) are employed to characterize the morphology of the fabricated nanobeam cavities. The measured transmission spectra indicate that the Q factor of deeply- etched nanobeam cavities surpass 5 × 103 with acceptable insertion loss of less than - 2 dB. These deeply-etched nanobeam cavities can find their applications in on-chip optical sensors or optical filters.