The invention provides a phenolic resin black function master batch and a preparation method thereof. The phenolic resin black function master batch is prepared from the following raw materials by weight: 200 parts of phenyl hydroxide, 148 to 152 parts of formaldehyde, 2 to 10 parts of a catalyst, and 4 parts of a composite functional black coloring agent. The preparation method comprises the following steps: first, adding molten phenyl hydroxide into a three-mouth beaker equipped with a stirrer, a condenser and a thermometer, adding formaldehyde according to the weight ratio, and carrying out stirring and heating to ensure that the temperature of the reaction system is 100 to 104 DEG C; adding the catalyst according to the weight ratio for a 1 to 2 hours' reaction when the liquid flows back; adding the composite functional black coloring agent according to the weight ratio when the liquid becomes turbid, carrying out a backflow reaction for 1.5 to 2 hours, dehydrating under decompression, carrying out a polycondensation synthesis reaction when the viscosity of resin reaches up to a certain value, discharging fast after the polycondensation synthesis reaction is finished, and carrying out cooling and smashing for treatment. The master batch is good in dyeing property and flowability, can be added with an optional quantity, and can be used for improving toughness effect and rising heat distortion temperature, so that the comprehensive performance is improved remarkably.