This standard specifies a method for the determination of benzo (a) pyrene [B (a) P] in water quality using acetylated filter paper chromatography Spectrophotometric method, spectrophotometry, suitable for drinking water, surface water, domestic sewage and industrial wastewater. The minimum detection concentration is 0.004 μg/L. Since B (a) P is a highly carcinogenic polycyclic aromatic hydrocarbon, this standard requires the wearing of gloves resistant to organic solvents during operation, and the operation should be carried out in a well-ventilated environment protected from direct sunlight. This method achieves accurate detection of B (a) P content in water by cyclohexane extraction and spectrophotometer determination.