The invention belongs to the field of high polymer materials and gallic acid-based thiol and a preparation method and an application thereof as well as a shape memory polymer (SMP) and a preparation method and an application thereof. The preparation method of the gallic acid-based thiol comprises the steps of 1, firstly mixing gallic acid, an acid binding agent and a solvent, adding 3-bromopropene, heating and reacting for 22-26 hours to obtain an intermediate product; 2, irradiating the intermediate product obtained in the step 1, thioacetic acid and photoinitiator for 20-60 minutes by usinga 200-500 W high pressure mercury lamp to obtain an intermediate product; and 3, finally, reacting the intermediate product obtained in the step 2 with a sodium hydroxide-methanol solution for 7-9 hours to obtain the gallic acid thiol. The gallic acid is used as a raw material of a sulfydryl-epoxy polymer and a positive reference value for broadening the application and increasing the added valueof natural polyphenol products is provided; and the bio-based sulfydryl-epoxy polymer is used as a shape memory material and positive promoting roles in expanding the types of shape memory materials and replacing petroleum-based similar products are played.