The use of glutaraldehyde in the fine chemical industry has resulted in a large number of glutaraldehyde products such as tanners, disinfectants, protein cross linkers, and tissue curing agents being discharged into water bodies, causing serious pollution to aquatic organisms and the eco environment and harm to the whole ecosystem. Therefore, it is essential to develop a rapid and simple detection technique for glutaraldehyde. Surface enhanced Raman spectroscopy (SERS), an established quantitative detection technique based on the scattering effect of light by the molecules to be measured, offers several advantages such as high sensitivity, low amount of sample required, and small water interference, which is highly functional and widely used in the field of analytical detection. The literature has reported no case for the quantitative detection of glutaraldehyde in environmental water bodies based on SERS technology. A surface-enhanced Raman spectroscopy method determining glutaraldehyde in water was developed based on the local surface plasmon resonance effect of gold nanoparticles, the enrichment and concentration of MIL-101(Cr), and the Schiff base reaction between PATP and glutaraldehyde. Au@MIL-101 was prepared by solution immersion method, and then the Au@MIL-101/PATP composite SERS substrate was obtained by modifying PATP on the surface of gold nanoparticles through the Au-S covalent bond. The substrate material is characterized by transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The effect of the density of Au nanoparticles in the composite substrate on the Raman enhancement effect was studied. The Au@MIL-101 material with chloroauric acid concentration at 0.6 g·L^-1 has the best enhancement effect. The Schiff base reaction between GA and PATP produces a characteristic peak of at 1 621 cm^-1. Good linearity between the ratio value of I_{1 078} to I_{1 621} and GA concentration was obtained in the range of 1×10^-7~1×10^-5 mol·L^-1 with the detection limit of 3.5×10^-8 mol·L^-1. This method is applied to detect glutaraldehyde in river water and tap water. The recovery rates of standard addition in tap water and river water were 91.4%~111.8%, 89.8%~114.2%, and the relative standard deviations were 5.2%~14.5%, 8.6%~13.4%, respectively. This method has the advantages of simplicity, rapidity, and environmentally friendly, which provides a new way for detecting trace glutaraldehyde in water.