The use of the refractive index as an endogenous label in 3D quantitative imaging for label-free biological samples is gaining popularity. However, some of the following improvements still need to be made: 1) a more accurate scattering measurement model should be established to improve the imaging resolution at the theoretical level; 2) there is still a necessity to overcome the limitation of sparse data, develop a more effective refractive index 3D reconstruction inversion algorithm, and improve the reconstruction accuracy and calculation speed; 3) as the refractive index is nonspecific for biological features, in-depth analysis of the refractive index in samples is required. At the application level, this study requires mature equipment to advance clinical procedures. Furthermore, its applications can be expanded to other domains of study, including water environment monitoring, food safety, material characterization, virology, and single-molecule analysis.