Abstract: In order to explore the pollution of VOCs and the characteristics of secondary generation and transformation in the atmosphere of southern Shandong Province, a Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS) was used to monitor the volatile organic compounds (VOCs) in the early summer atmosphere of six districts in a southern city of Shandong Province during May 19^th-27^th, 2021. The mass concentration, chemical composition, and contribution to the formation potential of ozone and secondary organic aerosols were investigated. The results showed that: (1) The average mass concentration of atmospheric VOCs in this city is 190.96 μg/m³, which are mainly composed of oxygen-containing compounds, hydrocarbons, halogenated hydrocarbons, benzene series and sulfur-containing compounds. The species with higher mass percentages are vinyl acetate, propionaldehyde, cyclohexanone, and pentene. (2) Oxygen-containing compounds and hydrocarbons are the most important ozone precursor gases here (except District A), and their contribution to ozone formation potential (OFP) is 50% and 40%, respectively. (3) Except toluene contributes the most to the formation potential of secondary organic aerosols in District C, xylene contributes the greatest potential to secondary organic aerosol formation (SOAFP) in other districts, and contributes more than 30% of the total SOAFP in each district. (4) Because there are many large chemical companies, the VOCs compositions in District A are quite different from those in other districts. Vinyl acetate and xylene are the main VOCs components, benzene series, oxygenated organics, halogenated hydrocarbons and hydrocarbons contribute equally to OFP of 25% separately. VOCs in District A have a higher SOAFP, which is about 1.5-2.0 times of those in other districts. (5) Through the specific species ratio, cruise monitoring and analysis, the VOCs in District A mainly come from solvent evaporation and combustion processes, the VOCs in District C mainly come from traffic, and the VOCs in other districts mainly come from combustion and industrial production processes; Food processing (such as oil fume) is also an important source. This study shows that reducing the concentration of oxygen-containing organics, hydrocarbons, and benzene series in the atmosphere is an effective way to control the generation of atmospheric ozone and secondary organic aerosols in cities.