To fight against infectious diseases (e.g., SARS, COVID-19, Ebola, etc.), government agencies, technology companies and health institutes have launched various contact tracing approaches to identify and notify the people exposed to infection sources. However, existing tracing approaches can lead to severe privacy and security concerns, thereby preventing their secure and widespread use among communities. To tackle these problems, this paper proposesCoAvoid, an edge-based, privacy-preserved contact tracing system that features good dependability and usability.CoAvoidleverages the Google/Apple Exposure Notification (GAEN) API to achieve decent device compatibility and operating efficiency. It utilizes Bluetooth Low Energy (BLE) to detect close contact with other people and leverages GPS with fine-grained matching algorithms to verify user information. In addition, to enhance privacy protection,CoAvoidapplies fuzzification and obfuscation measures to shelter sensitive data, making both servers and users agnostic to information of both low and high-risk populations. The evaluation demonstrates good efficacy and security of CoAvoid. Compared with four state-of-the-art contact tracing applications,CoAvoidcan reduce the size of upload data by at least 90% and reduce the verification time by 92%. More importantly,CoAvoidcan preserve user privacy and resist replay and wormhole attacks in all analysis scenarios.