Functional near-infrared spectroscopy (fNIRS) is a new and nondestructive detection technology that can effectively measure changes in cerebral hemoglobin concentration. The development of a high-performance wearable fNIRS system is of great significance for clinical diagnosis and daily life monitoring. This paper compares the components of different fNIRS systems. Firstly, the selection and arrangement of light source and photodetector in the system are analyzed and compared. Secondly, the methods of data acquisition, data preprocessing and data analysis are compared. Finally, the methods of improving the temporal resolution, spatial resolution and portability of the system are discussed. This article provides guidance for the reader in designing a high-performance fNIRS system.