The effects of conventional heating, ultrasonic, and microwave treatments on the stability and antioxidant activities of anthocyanidin standards (delphinidin and petunidin) were studied. The antioxidant activities of delphinidin and petunidin significantly decreased during the treatments, which suggested that the antioxidant activities of the degradation products were lower than that of anthocyanidin. In addition, the degradation of delphinidin and petunidin followed first‐order reaction kinetics. The kinetic parameters indicated that delphinidin was more stable than petunidin. The microwave treatment led to the fastest degradation, followed by the conventional heating and ultrasonic treatments. Moreover, three types of degradation products of delphinidin were found by HPLC‐Q‐TOF‐MS after all three treatments, and they were phloroglucinaldehyde, delphinidin chalcone, and 3,4,5‐trihydroxybenzoic acid. Petunidin was broken into phloroglucinaldehyde, petunidin chalcone, and 3‐methoxy‐4,5‐ dihydroxybenzoic acid. Practical applications Anthocyanins with great antioxidant activity are widely distributed in plants. The stability of the anthocyanin affects its antioxidant activity and bioavailability. When anthocyanins are degraded, their antioxidant activities change accordingly. Therefore, it is crucial to study the structure, stability, and antioxidant activity of anthocyanins. This paper explores the structures and pyrolysis pathways of delphinidin and petunidin and provides basic data for the utilization and preservation of anthocyanins during food processing and production.