The Sichuan Basin (SCB) is one of the regions suffering from severe air pollution in China, but fewer studies have been conducted for this region than the more developed regions in North and East China. In this study, a source-oriented version of the Community Multi-scale Air Quality (CMAQ) model was used to quantify contributions from nine regions to PM<sub>2.5</sub> (i.e., particulate matter (PM) with an aerodynamic diameter less than 2.5 μm) and its components in the 18 cities within the SCB in the winter (December 2014 to February 2015) and summer (June to August, 2015). In the winter, citywide average PM<sub>2.5</sub> concentrations are 45~126 μg m<sup>−3</sup>, with 21~51 % and 39~66 % due to local and non-local emissions, respectively. In the summer, 15~45 % and 25~52 % of citywide average PM<sub>2.5</sub> (14~31 μg m<sup>−3</sup>) are due to local and non-local emissions, respectively. Compared to primary PM (PPM), the inter-region transport of secondary inorganic aerosols (SIA, including ammonia (NH<sub>4</sub><sup>+</sup>), nitrate (NO<sub>3</sub><sup>−</sup>), and sulfate (SO<sub>4</sub><sup>2−</sup>)) is greater. The region to the east of SCB (R7) is the largest contributor outside the SCB, and it can contribute approximately 80 % in the northeast, east, and southeast rims of the SCB, but only 10 % in the other regions in both seasons. Under favorable transport conditions, regional transport of air pollutants from R7 could account for up to 35~100 μg m<sup>−3</sup> of PM<sub>2.5</sub> in each of the SCB cities in the winter. This study demonstrates that it is important to have joint emission control efforts among cities within the SCB and neighbor regions to the east in order to reduce PM<sub>2.5</sub> concentrations and prevent high PM<sub>2.5</sub> days for the entire basin.