The invention provides a method for synthesizing monopegylation fixed piont modification thymopoietin, which belongs to the field of biomedicine. According to the method, firstly, a solid phase is adopted for synthesizing TP5 containing protecting groups, the defect that the fluorenylmethyl chloroformate (FMOC) unit removal operation of the method in the prior art is difficult to carry out is avoided, then, the modified polyethylene glycol is connected onto the lysine side chain amino at the fixed point in a liquid phase, the goal of fixed point modification is reached, simultaneously, the space steric hindrance of the solid phase wang resin is avoided through the liquid phase environment, finally, all protecting groups are removed in one step through palladium carbon catalytic hydrogenation to obtain the pegylation thymopoietin with the long-action effect, the synthesis process is simple and convenient, the cost is low, the yield is high (the total yield is higher than 20 percent), and the industrial production is convenient. The pegylation thymopoietin synthesized by the method can not be easily hydrolyzed by esoteric protease, the renal clearance can be obviously reduced because the molecular weight is heavy, and the internal circulation time is greatly prolonged, so the goals of obviously prolonging the half-life period and improving the bioavailability of organisms are reached.