In the present research, the complete dissolution of carrageenan was realized by using NaOH aqueous solution and the corresponding mechanism was successfully revealed. The properties of carrageenan solution prepared in NaOH aqueous solution were comprehensively studied by gel temperature, differential scanning calorimetry and dynamic light scattering. The intra- and intermolecular interactions of carrageenan in NaOH/H2O system were studied by a combination of NMR measurements (including C-13 NMR and Na-23 NMR) and FTIR. The stability of carrageenan in NaOH aqueous solution was studied by the average molecular weight and viscosity determination. The results indicated that gel temperature and gel-sol transition temperature of carrageenan solution decrease with the dosage increasing of NaOH and a true and stable carrageenan solution was obtained by completely dissolving carrageenan in NaOH aqueous solution. The dissolution mechanism was that carrageenan chains were surrounded directly by NaOH hydrates to form hydrogen-bonded structure, leading to the good dissolution.