To address the demand for high-precision displacement measurement in Industry 4.0 and intelligent manufacturing environments, and to overcome the limitations of existing phase-based and RSSI-based RFID sensing methods, such as susceptibility to environmental noise, hardware instability, and challenges in complex industrial settings. This paper presents a high-precision displacement monitoring system, RCDS, leveraging the mutual coupling effect of RFID tags. The proposed system amplifies displacement-induced fluctuations in the RSSI waveform through a two-stage mutual coupling model, effectively enhancing the sensitivity to micro-scale changes. Additionally, an enhanced change-point detection algorithm, WaveAMP, is introduced, incorporating a two-stage dynamic fitting optimization strategy. Experimental results demonstrate that the system achieves millimeter-level displacement detection with an accuracy improvement close to 70% compared to current methods and reliably detects displacement changes as small as 3 mm.