The long-path differential optical absorption spectroscopy (DOAS) technique is used for monitoring HCHO, O3 and NO2 in Jiangmen City in the Pearl River Delta from Oct. 15 to Nov. 19, 2008. Combined with meteorological data, the analysis of major pollutants HCHO, O3, NO2 diurnal variation characteristics in Jiangmen City is made. At the same time, the main sources of pollution in Jiangmen City are analyzed. The correlation analysis and trend comparison of HCHO and other types of pollutants concentration data indicate that the source of HCHO in Jiangmen City comes mainly from secondary pollution. Results of multiple linear regression also confirm this conclusion.