Abstract: Copper ion (Cu²⁺) is a key trace metal in the ocean, and its mass concentration variation not only reflects the environmental status of marine ecosystems but also serves as an important geochemical indicator for deep-sea mineral exploration. To achieve efficient and selective detection of Cu²⁺ in seawater, a Cu²⁺ sensor based on surface plasmon resonance (SPR) technology was developed in this study. The sensor utilized a chitosan-modified gold film to enhance the selective binding of Cu²⁺, and incorporated a linear CCD array for high-resolution acquisition of SPR signals. Experimental results demonstrated that the system exhibits excellent sensitivity, selectivity, and stability in complex seawater environment, enabling rapid, in-situ, and real-time detection of Cu²⁺. This technique not only provides a novel approach for routine monitoring of Cu²⁺ in marine environment, but also offers an effective tool for the in-situ exploration of deep-sea mineral resources such as copper-rich crusts and hydrothermal deposits.