Abstract: The GNSS signals are weak, their signal structure is publicly available, making them vulnerable to spoofing attacks. These attacks can occur while the receiver maintains locked on the tracking loop and are often difficult to be detected in real time. To investigate the spoofing process and enhance defense mechanisms, this study analyzes the impact of spoofing signals on the delay-locked loop (DLL) of the receiver, particularly the code phase tracking process. Under the assumption of frequency-locking mode, the relationship between the relative code phase difference of the spoofing signal and the authentic signal, as well as the locally generated pseudo-random code, is derived. This relationship is also shown to depend on the spoofing-to-signal ratio (SSR). Theoretical results are verified through loop and GNSS receiver simulations, confirming the validity of the analysis. This research provides theoretical support for improving the security and defense capabilities of GNSS systems.