A paper sensor, a gold nanoparticles-based lateral flow immunochromatographic assay (GNPs-LFIA), was successfully established for the rapid quantitative detection of dibenz[a,h]anthracene (DBA) in drilling fluids (DFs). Computational analysis was employed to rationally design a novel hapten to effectively expose the active site of DBA, resulting in the successful development of a monoclonal antibody with high sensitivity and specificity. The half-maximum inhibitory concentration was 5.814 ng/mL. Then, the GNPs-LFIA was established following the optimization of the extraction agent and method. The limit of detection for DF samples was 0.273 mg/kg. Recovery experiments showed a high level of consistency with the results obtained by high-performance liquid chromatography-fluorescence detection, which indicated that the established GNPs-LFIA offered exceptional accuracy and reliability. Consequently, this method is well-suited for the rapid screening and determination of DBA in oilfield chemicals and presents a technical solution to identify polycyclic aromatic hydrocarbons.