An AIE-active fluorescent probe, MHTS, with good sensitivity and selectivity for the detection of Cu²⁺ was synthesized from myrtenal. The fluorescence intensity of MHTS at 542 nm indicated a good linear relationship with the concentration of Cu²⁺ in the range of 0–20 μM, and the detection limit was 1.25 × 10⁻⁷ M, which was far lower than the national standard of Cu²⁺ in drinking water. The interference experiment showed that other metal ions show no interference on the detection of Cu²⁺. The fluorescence of MHTS changed from yellow to colorless under a 365 nm UV light. The detection of Cu²⁺ was effective in the pH range of 3–8. Therefore, it can be used for the detection of Cu²⁺ in fresh vegetables and zebrafish.