A highly sensitive method was developed for the determination of 17 nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) in PM_2.5 using an ultrasound-assisted extraction (UAE)-online solid phase extraction (online SPE)-liquid chromatography-tandem mass spectrometry (LC/MS). The method underwent comprehensive optimization, encompassing UAE solvents and times, extract filtering, online SPE condition and LC/MS condition. Isomeric separation and detection of mononitro-PAHs, dinitro-PAHs, and OPAHs were achieved based on the proposed MS/MS fragmentation pathway in negative mode atmospheric pressure chemical ionization. Taking the advantage of online SPE, the method achieved lower limits of detection (NPAHs: 0.001 ~ 0.042 μg L⁻¹, OPAHs: 0.01 ~ 0.038 μg L⁻¹). Recovery ranged from 64% ~ 108% at three spiking levels (0.25, 1.0 and 10.0 μg L⁻¹) with the relative standard deviations (RSDs) of 3% ~ 23%. This study represents first application of LC/MS methodology for the quantification of three carcinogenic dinitro-PAHs (1,3-dinitropyrene, 1,6-dinitropyrene, 1,8-dinitropyrene) in atmospheric PM_2.5. The established method was successfully employed to determine the wide range concentrations of various NPAHs and OPAHs (∑NPAH: 9.4 ~ 303.3 pg m⁻³, ∑OPAHs: 125.2 ~ 1948.1 pg m⁻³) in PM_2.5 samples collected in Beijing during the summer and winter seasons.