An onion seed fine-selection method is mainly as follows: placing onion seeds after winnowing and drying in a container with clean water, stirring well, then standing for 5 to 20 minutes, removing seeds and impurities floating on the surface of the solution; agitating the solution in the wide-mouth container along same direction, using an 18 mesh colander to dragging most of the seeds out of the solution, using an 18 mesh gauze sieve to filter the solution, wherein 1cm deep of the solution is left in the wide-mouth container, and merging seeds on the gauze sieve and the seeds dragged out by the colander; using the 18 mesh gauze sieve to filter the remaining solution, merging onion seeds on the gauze sieve and the merged seeds, packing into a 18 mesh gauze bag, then putting into a washing machine for dehydration for 3 minutes, and drying in air to a moisture content of 8% to obtain finely-selected onion seeds. The method can effectively eliminate onion seeds which are rotten, damaged by worms and poor in plumpness, and have other damages and impurities, and the germination rate of the finely-selected onion seeds is 1.63-15.43% higher than the germination rate of onion seeds selected by winnowing methods in the prior art.