Abstract: Recently heavy air pollution episodes have frequently happened in many cities of China, which attracts much social public attention. Limited researches on characteristics of PM_2.5 and source apportionments during the heavy pollution process in China have been reported in publications. This study aimed to deeply understand characteristics of PM_2.5 and source contributions during the heavy pollution process in typical cities of China. The ambient PM_2.5 samples were collected in Urumchi City from 19^th-30^th, January, 2013. Based on the Technical Regulation on Ambient Air Quality Index (on trial), heavy pollution episodes were identified based on data of mass concentrations from 19^th-28^th, January. The PM_2.5 and main chemicals (e.g., water solvent ions, inorganic elements and carbon species) were analyzed and presented by correlation analysis to identify the characteristics of PM_2.5. The enrichment factor was used to assess contributions of crustal and anthropogenic sources. The source apportionment of PM_2.5 was conducted via the CMB model. The results showed that the average mass concentration of PM_2.5 was over than the National Air Quality Standard. The PM_2.5 concentration was the highest at the site of Midong Environmental Protect Agency, followed by sites of Tielu Agency and Monitoring Station. SO₄^2-, TC, Si and NO₃^- were the main chemical compositions and secondary ions accounted for 43.1% in PM_2.5. Resuspended dust, coal combustion dust and secondary particles were the main contents of the ambient PM_2.5, with contributions of 24.7%, 15.6% and 38.0% in the urban area of Urumchi City and 20.8%, 28.0% and 36.2% in Midong District, respectively, while the corresponding contributions of secondary sulfate were 28.6% and 27.0%.