The invention discloses an ultra-high performance liquid chromatography method for determining the molecular size distribution of human serum albumin. The method comprises the step of determining themolecular size distribution of the human serum albumin by means of ultra performance liquid chromatography. In the ultra high performance liquid chromatography analysis, ACQUITY UPLC PROTEIN BEH SEC Column and a chromatographic column with 200 angstrom, the particle size of 1.7 micron, the column length of 150 mm and the column diameter phi of 4.6 mm are adopted, the column temperature is room temperature, a PBS buffer solution with the mobile phase of 0.2 mol L<-1> and the flow rate of 0.6 ml min<-1> is adopted, a Waters UPLC TUV ultraviolet detector is used for collecting data at 280 nm, thesample injection volume is 10 microliters, the volume of a strong probe washing solution is 200 microliters, the volume of a weak probe washing solution is 600 microliters, and a quantitative loop option is partial loop with needle overfill. According to the UPLC method for determining the molecular size distribution of the human serum albumin in the research, compared with original HPLC methods,the detection speed is increased by more than 10 times, and the chromatographic response is increased by more than 5 times. The UPLC method for determine the polymer content of a human serum albuminproduct is high in detection speed, simple and good in repeatability. The UPLC method helps to achieve high-throughput determination of human serum albumin multimers, and the efficiency of testing thehuman serum albumin is substantially improved.