Position and time information provided by Global Satellite Navigation System (GNSS) is used in many application fields importantly. However, the satellite navigation signal is vulnerable to interference signals due to the low signal strength and susceptible to attacks motivated by economic, military and security reasons. The most common attack is jamming. As attacks become more sophisticated, they are expected to evolve to spoofing. Spoofing is a larger threat because the receiver cannot recognize that they are being targeted by an attacker. For this reason, it is becoming more important to monitor GNSS signals continuously in order to enhance the reliability of GNSS signals. To ensure the safe use of satellite navigation signals in the future, it is necessary to prepare for spoofing attacks. It is possible to reduce the damage to users of satellite navigation by early detection of the spoofing signals. The detection method should be applied according to the attack method, and various detection methods should be applied because the impact of the attacker on the receiver may vary depending on the attack method and attack item. In this study, the spoofing detection method for GNSS augmentation system is proposed. The spoofing detection is made to the whole system by considering the reference station and user receiver, respectively. In the reference station, an advanced and comprehensive method is proposed for overcoming the limitations of each individual detection algorithm. In the user receiver, the method of monitoring measurement variation continuously is proposed. The proposed detection method is advantageous in that it can be applied to a receiver directly because the spoofing signal can be detected without being equipped with additional hardware in a conventional receiver. The proposed methods enhance the performance of spoofing detection and increase the reliability of the satellite navigation system.