The widespread application and deployment of Wi-Fi technology has spawned many Wi-Fibased indoor positioning technologies. In recent years, WiFibased device-free positioning algorithm has attracted the attention of researchers. The device-free positioning algorithm does not require the target object to carry the wireless transmission device, but instead estimates the target object’s position by measuring the impact of the target object on the wireless signal transmission. Because it does not need the target to carry the relevant equipment, it can be widely used in many occasions such as elderly health care. Existing device-free positioning technologies usually require pre-acquisition of training data, so they are easily affected by the indoor complex and changeable environments to result in the degradation of localization accuracy. This paper proposes a device-free localization algorithm based on line-of-sight path detection. By using the Channel State Information (CSI), we can determine whether the path between a pair of wireless transceivers is a Line of Sight (LoS) path. On this basis, we propose a new devicefree positioning algorithm. The algorithm deploys a set of Wi-Fi transceivers in the monitoring area. For any pair of wireless devices, we determine whether the target object is within the Fresnel zone of the device by identifying whether there is a line-of-sight path between them or not. We propose a polling-based approach to get the most probable location of the target. The experimental results on the actual equipment show that the proposal can achieve an accuracy of about 0.5 meters, does not require  prior training, and has higher real-time performance.