Abstract: The analysis of discolored substances in groundwater remains a challenging issue in the field of environmental monitoring. Traditional analytical methods have limitations such as poor timeliness and complex operation. This study established an on-site analysis method for discolored substances in groundwater based on solid-phase microextraction combined with portable gas chromatography-mass spectrometry (SPME-PGC-MS). Based on a typical scenario of discolor pollution spreading to rivers from a surrounding enterprise, qualitative screening and quantitative determination of key substances were performed on groundwater samples simultaneously. Through qualitative screening, it was determined that the main discolored substances in groundwater are aniline derivatives, including aniline, N, N-dimethylaniline, N-ethylaniline, N-ethylo-toluidine and N, N-diethylaniline. Further relying on qualitative screening results, the main source of river pollution was confirmed. Meanwhile, the method showed good quantitative linearity for aniline compounds (R²>0.98), with recovery rates ranging from 93.81% to 107.77%, relative standard deviations of 6.23% to 10.31%, and the detection limits of 0.44 to 0.63 μg·L^-1. Through quantitative analysis, the diffusion range of pollutants can be accurately identified, and N-ethylaniline can be determined as a characteristic marker of local area discolor pollution. The SPME-PGC-MS technology developed in this study provides a new approach for rapid investigation and monitoring of groundwater pollution. It can effectively overcome the limitations of traditional technology, such as poor timeliness and high cost, and provide important data support for the formulation of subsequent groundwater risk control measures for the site. It is expected to become a core technical means for emergency response, early warning, and long-term monitoring of groundwater pollution.