The invention discloses a macromolecular polymerizable photoinitiator and a preparation thereof. The method comprises the following steps of: adding 4-hydroxybenzophenone and methanal to a three-necked flask, heating to 95 DEG C, reacting for 2 hours, heating to 150DEG C, leaching under at reduced pressure for 20 minutes, cooling to 105 DEG C, collecting products, pouring products into water, leaching to obtain a macromolecular photoinitiator, dissolving the macromolecular photoinitiator in an organic solvent, dissolving epoxy chloropropane in the solvent under catalysis of boron trifluoride,dropwise adding mixed liquid, reacting at a temperature of 0-5 DEG C, then stirring for 3 hours at a temperature of 70 DEG C, removing epoxy chloropropane and solvent, dissolving residues with a solvent, adding alkali and reacting for 0.5 hour at a temperature of 40 DEG C, removing salt and the solvent, re-dissolving residues with a solvent, washing with water and drying, adding crylic acid, p-hydroxyanisole and tetrabutylammonium bromide, heating for reacting for 6 hours, and then removing the solvent so as to obtain macromolecular polymerizable photoinitiator. The macromolecular polymerizable photoinitiator prepared by the method has the advantages of large molecular weight, weak mobility and good polymerizability.