Copper is a trace element in mammalian nutrition, and it is essential to daily intake of 1.5-2.0 mg of copper. However, excessive intake of copper can cause toxicity to the human body, so it is very important to quantitative analysis copper levels of serum and urine in early diagnosis of certain diseases. In this paper, based on the strong fluorescence quenching effect of Cu²⁺ on nitrogen-sulfur-doped graphene quantum dots, a rapid, highly sensitive and reliable method was established, the limit of determination is 2.708 nmol/L. Variable temperature experiments and thermodynamic calculations were explored to discuss the mechanism of fluorescence quenching, results show that the quenching process is static quenching process.