A fiber-grade polyphenylene sulfide resin synthesis method, characterized in that the method uses sodium bisulfide and p-dichlorobenzene as raw materials, N-methyl pyrrolidone as a solvent and C5-C6 fatty acid sodium salt as a polymerization additive for synthesis through polymerization, the method being characterized in the following reaction steps: adding NMP, 40%-50% NaOH solution and C5-C6 fatty acid into the reactor for heating to the temperature of 90-120°C simultaneously with mixing and nitrogen protection at the velocity of 1.0∼2.0°C/min; proceeding with heat preservation for 1-3 hours before prior to further heating to temperature of 180∼200°C at the velocity of 1.0∼2.0°C/min for dehydration; reducing temperature to 110-130°C after dehydration; adding NaHS solution and NMP into the reactor following Step for heating to temperature of 180∼200°C at the velocity of 0.7∼1,5°C/min simultaneously with mixing and nitrogen protection prior to dehydration; further reducing temperature to 140∼160°C when water content in the system is below 1.0mol/mol sulfur; adding PDCB and NMP into the reactor following Step for heating to the temperature of 220∼240°C within 1.0-1.5 hours prior to heat preservation for 1-3 hours; further proceeding with heating to temperature of 260∼280°C at the velocity of 1.0∼1,5°C/min prior to heat preservation for 1-3 hours; once completed, reducing temperature to 130∼150°C within 0.5-1 hour to obtain PPS reaction slurry; Proceeding with centrifugation of PPS reaction slurry as obtained through Step, then leaching with 130∼150°CNMP of the same mass as the filter cake; further proceeding with leaching with hydrochloric acid solution of the same mass as the filter cake prior to mixing and collection of all filtrate; Repeatedly washing the filter cake as obtained in Step with 70-100°C deionized water until the chlorine ion is acceptable; further drying the filter cake to obtain polyphenylene sulfide resin; and Agitating and mixing the filtrate as obtained in Step for separation of C5-C6 fatty acid through azeotropic rectification in the rectification device with water separator; proceed with further rectification to remove the moisture; finally, proceeding with depressurized distillation for recycling of solvent NMP. adding NMP, 40%-50% NaOH solution and C5-C6 fatty acid into the reactor for heating to the temperature of 90-120°C simultaneously with mixing and nitrogen protection at the velocity of 1.0∼2.0°C/min; proceeding with heat preservation for 1-3 hours before prior to further heating to temperature of 180∼200°C at the velocity of 1.0∼2.0°C/min for dehydration; reducing temperature to 110-130°C after dehydration; adding NaHS solution and NMP into the reactor following Step for heating to temperature of 180∼200°C at the velocity of 0.7∼1,5°C/min simultaneously with mixing and nitrogen protection prior to dehydration; further reducing temperature to 140∼160°C when water content in the system is below 1.0mol/mol sulfur; adding PDCB and NMP into the reactor following Step for heating to the temperature of 220∼240°C within 1.0-1.5 hours prior to heat preservation for 1-3 hours; further proceeding with heating to temperature of 260∼280°C at the velocity of 1.0∼1,5°C/min prior to heat preservation for 1-3 hours; once completed, reducing temperature to 130∼150°C within 0.5-1 hour to obtain PPS reaction slurry; Proceeding with centrifugation of PPS reaction slurry as obtained through Step, then leaching with 130∼150°CNMP of the same mass as the filter cake; further proceeding with leaching with hydrochloric acid solution of the same mass as the filter cake prior to mixing and collection of all filtrate; Repeatedly washing the filter cake as obtained in Step with 70-100°C deionized water until the chlorine ion is acceptable; further drying the filter cake to obtain polyphenylene sulfide resin; and