In order to investigate the key aroma compounds of Camellia sinensis var. assamica cv. Duntsa black tea and their formation mechanism during processing, this study utilized headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) to systematically analyze the volatiles in fresh leaves (XY), shaking (YQ), withering (WD), rolling (RN), fermentation (FJ), initial drying (CH), and finished product (CP). Principal component analysis (PCA) and orthogonal partial least squares-discrimination analysis (OPLS-DA) with permutation tests were performed. Key aroma compounds were identified using relative odor activity value (rOAV) and aroma character impact (ACI). Results revealed that during the processing, 107 volatile compounds were identified in the tea samples of Camellia sinensis var. assamica cv. Duntsa black tea primarily comprising alcohols, esters, and alkenes. During the whole processing process, the relative content of alcohols, esters and others showed a fluctuating downward trend. The relative content of aldehydes, ketones and olefins showed a fluctuating upward trend. The PCA and OPLS-DA models based on the relative content of aroma substances could effectively distinguish different processing samples. Further screening, with VIP>1, rOAV>1 and ACI>1% as the conditions determined that linalool, methyl salicylate, geraniol, hexyl hexanoate, trans-nerolidol and other five components together constituted the aroma quality of the sweet type of Camellia sinensis var. assamica cv. Duntsa black tea. The relative content of linalool, geraniol, and hexyl hexanoate showed an initial increase followed by a decline, peaking during the rolling stage at 382.74, 123.32, and 35.43 mg/L respectively. The relative content of trans-nerolidol showed a fluctuating upward trend, increasing by 22.60%. The relative content of methyl salicylate showed a fluctuating decrease, peaking at 252.95 mg/L during the rolling stage. The results of this study can provide a theoretical reference for the analysis of the aroma quality of Camellia sinensis var. assamica cv. Duntsa black tea.