As the core technology of distributed fiber-optic sensing, optical reflectometry may realize the non-destructive measurement at a remote position. It can be used to retrieve the distributed information such as reflectance, refractive index, polarization state along the optical fiber, and to diagnose the irregular "event" on fiber-optic links. For some high-end fields, such as the fault diagnosis on the fiber-to-the-home (FTTH) access network, the deformation monitoring on large generating units and large transformers, and the security monitoring on structures of airplane wings, the requirements on spatial resolution and measurement range of the sensing technologies are very high. In this paper, we summarized the research status on state-of-art optical reflectometry technologies, and reviewed the advances of key technologies on optical reflectometry with ultra-high spatial resolution and long measurement range. We proposed three different methods to improve the performance, and tried to promote their applications on distributed fiber-optic sensing systems.