The global navigation satellite system (GNSS) is a commonly used positioning solution, which provides users with worldwide precise location information with multiple positioning satellites. Due to the satellite signals being blocked and absorbed in the deep urban or indoor environment, the conventional navigation solutions are not precise enough for positioning in these areas. Navigation via signal of opportunity (NAVSOP) achieves users positioning by receiving and processing the signals already existed in the environment, which has been attracting significant attention in academic fields for its advantages in overcoming the problems. Common positioning methods used for NAVSOP are summarized, and their applicability in different systems is also analyzed. Technical features and research status for different NAVSOP are represented in detail. Aiming at the problem that the single navigation system has poor robustness, the advantages of application fusing NAVSOP into an integrated navigation system are analyzed from the system operating mode and other aspects. Finally, the existing problems in this field are indicated, and development tendencies of NAVSOP are also expected.