OBJECTIVE To understand the pollution level of polycyclic aromatic hydrocarbons(PAHs) in community fine particulate matter(PM_(2. 5)) in Lanzhou community, and assess the risk of cancer. METHODS Samples of atmospheric fine particles were collected in communities A and B of Lanzhou City from 10 to 16 of each month in 2018. The mass concentration and composition of 16 kinds of optimal control to the EPA PAHs, such as naphthalene(Nap), acenaphthylene(Acy), philippines(Phe), acenaphthene(Ace), fluorene(FI), anthracene(Ant), fluoranthene(Flu), pyrene(Pyr), chrysene(Chr), benzo(a) anthracene(BaA), benzene(b) fluoranthracene(BbF), benzene(k) fluoranthracene(BkF), benzo(a) pyrene(BaP), dibenzene(a, h) anthracene(DahA), benzene(g, h, i) perylene(BghiP) and indene(1, 2, 3-cd)pyrene(IcdP), were analysed, and the toxicity were assessed by toxicity equivalent concentration and lifetime excess carcinogenic risk(ECR). RESULTS The annual average PM_(2. 5) concentrations in community A and B were 70 μg/m~3, 2 times the national standard. The average annual PAHs concentrations in community A and B were 113. 56(5. 22-485. 71) and 55. 68(2. 39-257. 43) ng/m~3, respectively. In addition, in winter, spring and autumn, the PAHs of the two communities were mainly 3-5 rings, 3-ring and 6-ring PAHs were the main components in summer. The result of feature ratio method were shown that BaP of 16 kinds of PAHs was the equivalent mass concentration(BaPeq) range of 0. 00017-3. 19 ng/m~3, ΣBaPeqin community A and B were 7. 64 and5. 11 ng/m3, respectively. BaP and DahA were the most toxic, All of them contributed more than 70% to ΣBaPeq, the total ECR of Σ16 PAHs in community A and B were 6. 64×10~(-4) and 4. 44×10~(-4), respectivel. CONCLUSIONS BaP and DahA have certain potential health risks to residents in communities a and B of Lanzhou.