Abstract: In order to meet the needs of determination of trace polycyclic aromatic hydrocarbons(PAHs) in PM2.5 with small flow sampling, a method of gas chromatography-triple quadrupole mass spectrometry(GC-MS/MS) with ultrasonic extraction was established for the determination of 16 polycyclic aromatic hydrocarbons(PAHs) in PM2.5. The parameters were studied, like as the effect of different ion source temperature, the performance of the method, the collision voltage and the adaptability of this method by detecting the actual samples. Results show that the correlation coefficients of 16 PAHs in PM2.5 are 0.995-0.999. The recoveries of 16 PAHs are 84.4%-111% and 82.2%-95.3% for blank membrane samples and actual samples respectively, the precision is less than 10%. When the sampling volume is 24 m³，the limit detections of 16 PAHs are 0.007 5-0.063 ng/m³. Through the detection of the actual samples analysis (the concentration of PAHs ranged from 0.04-1.04 ng/m³ (in summer) and 0.2-30 ng/m³ in winter), the method has low detection limit and strong anti-interference ability with complex matrix, which can completely suitable for determination of PAHs in PM2.5.