Fentanyl is a highly lethal emerging drug that requires urgent rapid trace detection. In this work, high‐sensitivity detection of fentanyl is achieved by Au‐ and S‐doped reduced graphene oxide (Au@S‐rGO). Spherical electron microscopy revealed that Au and S existed in an atomically dispersed state. The possible configurations of S in Au@S‐rGO, as well as the effects of different doping positions on the electron density of Au, are analyzed by Density functional theory (DFT) simulations. The co‐modification of metal and nonmetal atoms significantly improves the catalytic activity of the electrode. The optimal electrode delivers a good linear relationship for fentanyl concentrations from 0.0291 to 38.2 µmol L‐1, with a detection limit of 9.7 nmol L‐1. The recovery rate of fentanyl in human serum ranged from 98.0% to 104%, demonstrating the precision of the sensor in real biological matrices. Furthermore, by employing rats in place of drug addicts, the coincidence rate between the electrochemical test results and the mass spectrometry results was 85.7% ~ 93.6%. Compared with mass spectrometry, the sensor offers faster, simpler, and more cost‐effective onsite detection. In summary, the novel diatomic catalyst design looks excellent for fabricating electrochemical sensors for the rapid detection of fentanyl in real samples.