The study of transformation mechanisms of volatile terpenoids in hybrid citrus can help to reveal the aroma formation of hybrid citrus and improve the quality and flavor of processed hybrid citrus products. The pulp of three kinds of hybrid citrus, namely, Orah mandarin, Harumi tangor, and Ehime No. 38, were used as the study objects. The qualitative and quantitative analysis of terpenoids in three hybrid citrus was carried out by head space-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). A total of 16 terpenoids, including 3 terpenes (D-limonene, γ-terpinene, p-1,3,8-menthatriene), 7 terpenoid alcohols (linalool, p-2,8-menthadien-1-ol, terpinen-4-ol, α-terpineol, carveol, nerol, citronellol), 4 terpenoid ketones (6-camphenone, dihydrocarvone, L-carvone, isopiperitenone) and 2 other oxygenated terpenoids(rose oxide, perillyl aldehyde), were detected in the three varieties of hybrid citrus, and D-limonene and α-terpineol were detected in all the three varieties of hybrid citrus. Transformation reactions were simulated using standards of the detected terpenoids under the acid and enzymatic environments of the pulp of the three varieties of hybrid citrus. The results revealed that there were inter-transformation relationships among the 10 terpenoids under acid catalysis. Under enzyme catalysis, interconversion relationships existed among 12 terpenoids. Possible transformation mechanisms were proposed according to their transformation pathways. The study could provide a theoretical basis for the optimization of aroma preservation and aroma enhancement processes for processed products of hybrid citrus.