Abstract: Dechlorane plus compounds are present at trace levels (ng/g) in sludge samples. The complex sludge matrix poses a significant challenge for the analysis of these compounds. To address this issue, this paper establishes an analytical method for determining dechlorane plus compounds in the sludge of sewage treatment plants, combining microwave-assisted extraction with gas chromatography-triple quadrupole tandem mass spectrometry. Sludge samples are processed using microwave-assisted extraction with online purification, using acetone-n-hexane (1∶1, V/V) as the extraction solvent. After extraction, GCB/PSA solid-phase extraction columns are used for further purification to reduce matrix interference. The multiple reaction monitoring (MRM) mode of mass spectrometry is employed for accurate quantification. This method demonstrates good linearity (r≥0.998) in the 5-400ng/mL range, with a detection limit of 0.017-0.040ng/g. The average recoveries were 79.8%-99.5%, 86.2%-104.8% and 91.2%-106.1% at low, medium and high concentrations, respectively, with relative standard deviations ＜6%. When applied to 11 sewage treatment plants, dechlorane plus compounds were detected, and the contents are relatively high (31.4-195.6ng/g). In sludge, average f_syn of syn-DP is 0.27, lower than that of DP products. This is due to stronger anti-DP adsorption or preferential syn-DP biodegradation When the A²/O process is adopted, the concentration of dechlorane plus compounds is significantly reduced, and the f_syn value is significantly increased, but the influencing mechanism still needs to be further explored. The BRIEF REPORT is available for this paper athttp://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202409190197.