As the most important component of deep red pigments, alkannin is investigated theoretically in detail based on time-dependent density functional theory (TDDFT) method. Exploring the dual intramolecular hydrogen bonds (O1-H2 center dot center dot center dot O3 and O4-H5 center dot center dot center dot O6) of alkannin, we confirm the O1-H2 center dot center dot center dot O3 may play a more important role in the first excited state than the O4-H5 center dot center dot center dot O6 one. Infrared (IR) vibrational analyses and subsequent charge redistribution also support this viewpoint. Via constructing the SI-state potential energy surface (PES) and searching transition state (TS) structures, we illuminate the excited state double proton transfer (ESDPT) mechanism of alkannin is the stepwise process that can be first launched by the O1-H2 center dot center dot center dot O3 hydrogen bond wire in gas state, acetonitrile (CH3CN) and cyclohexane (CYH) solvents. We present a novel mechanism that polar aprotic solvents can contribute to the first-step proton transfer (PT) process in the SI state, and nonpolar solvents play important roles in lowering the potential energy barrier of the second-step PT reaction.