We experimentally demonstrated a chemical sensing system for Cu2+ detection based on an optofluidic laser. A Fabry–Perot cavity within a square quartz capillary fluidic channel was built to enable optofluidic lasing. Rh6G-HS (Rh6G, hydrazine hydrate, salicylaldehyde), a rhodamine derivative was used as the laser gain medium, and the switching mechanism of spirolactam (fluorescence: “off”) to ring-opened amide (fluorescence: “on”) was used to provide strong fluorescence emission with the addition of Cu2+ ions. As the Cu2+ ion concentration increased, the optofluidic laser slope efficiency was enhanced and the lasing threshold was reduced. Under optimized conditions, the chemosensor exhibited a detection limit of $300~\mu \text{M}$ and satisfactory selectivity toward Cu2+ ions over other metal ions. This method may provide a new way to detect metal ions and could be applied to new applications in environmental protection and biochemical research.