As mobile computing technology becomes more and more mature, people feel great interest on contextaware applications and services. Referring to context, location-aware system is one of the most important components. This paper presents a precise indoor RFbased (IEEE 802.11) locating system named Precise Indoor Locating System (PILS). In order to acquire high level of location estimation result, a large number of training samples should be collected in offline phase. As a result, the system becomes impractical and huge number of man-power is needed. In this paper, we aim to reduce the manual effort in constructing radio map and maintain high accuracy in our system. We propose models for data calibration, interpolating, location estimation, and tracking in PILS. Wireless Channel Propagation model is also in our concern. Large scale and small scale fading are involved in the wireless channel propagation.