The invention relates to a synthesis method for a compound 5,10,15,20-tetra-(3,5-dihydroxy phenyl) porphyrin of water-soluble porphyrin shown in the formula I. The synthesis method includes the following steps that mixed acid of propionic acid/acetic acid is used as a reaction solvent, 3,5-dihydroxy benzaldehyde reacts with pyrrole (for example, 30 min or above, preferably, 40 min or above, such as 30 min-3 h, and preferably, 40 min-1 h) under heating reflux (for example, 115-125 DEG C, and for example, about 120 DEG C), reduced pressure distillation is conducted after the reaction, the mixed acid is removed, separation is conducted through a column chromatography method, recrystallization purifying is conducted, and 5,10,15,20-tetra-(3,5-dihydroxy phenyl) porphyrin is obtained. The formula I is shown in the description.