Abstract: To assess the condition of phthalic acid esters(PAEs) held up in the environment,and predict its biodegradability and provide basic data for sludge treatment and disposal,the aerobic biodegradation characteristics of six PAEs in the sewage sludge was investigated,and a model of the quantitative relationship between aerobic biodegradability and chemical structure(QSBR) was established.The results show that the degradation of six PAEs in the sludge conforms to the first-order reaction kinetic equations.Their biodegradability decreases with the increase of the carbon numbers of alkyl chains,and the steric factor represented by molecular connection indexes is an important parameter affecting the aerobic biodegradability of the tested PAEs in the sludge.