A method of making a thermally curable solder-resistant ink, which comprises the following steps: polymerizing an aliphatic diamine monomer having a long carbon chain, an aromatic dianhydride monomer, an aromatic diamine monomer having a carboxylic acid group, and an anhydride monomer having a carboxylic acid group in an aprotic solvent to obtain a polyamine acid; cyclizing the polyamine acid to obtain a polyimide; and mixing the polyimide and a curing agent to obtain the thermally curable solder-resistant ink. By the steps mentioned above, the thermally curable solder-resistant ink made from the method has a dielectric constant less than 3.00 and a dielectric loss less than 0.01 and thereby is applicable to high frequency electronic equipments. Also, the thermally curable solder-resistant ink has good electrical properties, folding endurance, solder resistance, warpage resistance, flame resistance, acid endurance, alkali endurance, good solvent resistance and low water absorption.