<p>Flat peach (<i>Prunus persica</i> L. Batsch. var. <i>Compressa</i> Bean) is a climacteric fruit and is, as a result, susceptible to deterioration. This study aims to effectively monitor the quality of flat peaches by measuring the representative quality indices and identifying key volatile compounds correlated with quality changes. The six quality indices of flat peaches (sensory evaluation, firmness, soluble solid content (SSC), titratable acid (TA) content, SSC/TA, and vitamin C (Vc)) were analyzed during storage at 4 ℃. The quality of the flat peach samples was divided into two grades using cluster analysis (CA) and principal component analysis (PCA). Moreover, the volatile compounds in the samples were analyzed in situ using solid-phase microextraction coupled with gas chromatography–mass spectrometry (SPME–GC–MS). Additionally, an orthogonal partial least square–discriminant analysis (OPLS–DA) model was established to identify variations in volatile compounds in different quality flat peaches. Finally, a total of 37 volatile compounds were identified, and 13 key aroma components were screened out. These key volatile compounds could effectively differentiate the quality of the flat peach samples. The results were consistent with the grading results from the quality indices. Among them, methyl hexanoate, (<i>Z</i>)-3-hexenyl acetate, <i>β</i>-ocimene, and linalool were closely related to the variation of peach quality and could be used as characteristic volatile compounds to evaluate the quality of flat peaches. These results are expected to provide a theoretical basis for the detection and quality evaluation of flat peaches in cold storage using quality indices or volatile compounds.</p>