Four drying methods were used to dehydrate white onions to explore the effects of different drying processes on their quality and flavor, including heat pump 55? °C - hot air 60?°C (HPD55? °C?HAD60 ℃), heat pump 60? °C- hot air 60 ?°C (HPD60?°C?HAD60℃), heat pump 60 ?°C (HPD), and vacuum freeze drying (FD). The drying characteristics, physicochemical traits and volatile aroma components were systematically investigated. It was demonstrated that drying time was reduced by 25% for HPD60 ℃-HAD60 ℃ in comparison with HPD. FD onions presented the optimal color as well as the maximum retention of total phenols and total flavonoids, while HPD60 ℃-HAD60 ℃ samples ranked next to FD in comprehensive quality. Drying remarkably increased umami, saltiness and sourness and decreased astringency of the samples according to electronic tongue analysis; Onions processed by HPD60 ?°C?HAD60 ?°C presented a milder overall flavor. 128 volatile flavor compounds were identified via gas chromatography?ion mobility spectrometry (GC?IMS), classified into 10 categories. The content of volatile substances in dehydrated onions was approximately 2~3 times that in fresh onions. Among them, FD?dried onions had the highest content (97.45?μg·g-1) and the highest level of sulfur?containing compounds, whereas the other three dehydrated onion samples were rich in alcohols, aldehydes, and ketones. Diallyl disulfide, (Z)?1?propenyl propyl disulfide, and isopropyl disulfide were the major flavor?contributing compounds of onions via odor activity value (OAV) analysis. Principal component analysis (PCA) demonstrated significant flavor differences between fresh onions and FD?dried onions, as well as between FD?dried onions and the other three dried onion samples. While the similar flavor profiles were observed between HPD60 ℃?HAD60 ℃ and HPD55 ?℃?HAD60 ℃ onions. Considering comprehensive efficiency, product quality and flavor characteristics, the combined drying process of HPD at 60 ℃ coupled with HAD at 60 ℃ exhibits promising potential for industrialized application. Combined with electronic tongue, OAV and PCA analyses, GC?IMS was proven to effectively distinguish flavor differences accross the samples subjected to four drying processes. These findings provide a theoretical basis for quality evaluation and flavor regulation of dehydrated onions.