Abstract: PM_2.5 is the primary pollutant which has influenced the urban atmospheric environment in recent years, and its genetic mechanism is complicated. The microscopic morphology and trace element concentration of PM_2.5 in the Guangzhou urban area were determined by Scanning Electron Microscope and Inductively Coupled Plasma-Mass Spectrometry, respectively. The enrichment factor method was adopted to constrain the source of PM_2.5. The results show that PM_2.5 mainly occurs as amorphousness fine particles. A silicate combination containing Fe, Mg, Al, K and Na is the main chemical composition of PM_2.5, characterized by the first fine particles from road dust and buildings. An energy spectrum diagram of single amorphous particle shows the combination characteristics of sulfate and nitrate. These particles may have been secondary fine particles formed from pollution gases of SO₂ and NO_x from automobile exhaust in the atmospheric environment, through the nucleation induced phase behavior change under specific physical and chemical conditions. Heavy metals were highly enriched in PM_2.5, including Cd, Se, Zn, Cu, Pb, and As. Local widespread use of deca bromine biphenyl ether as a flame retardant and a large number of E-waste dismantling are the main factors for abnormal enrichment of Br in the fine particles. The concentration of rare earth elements ranges from 0.022 to 0.582 ng/m³, with the relative enrichment of heavy rare earth elements in PM_2.5. These features indicate that the composition of PM_2.5 in the Guangzhou urban area are not only made up of primary particles, but also made up of secondary particles, characterized by multiple sources.