In order to investigate genetic diversity in populations of Flowering Chinese Cabbage and screen suitable sample size for germplasm regeneration, different bulks with 10,15,20,25,30,35 and 40 plants were formed from an accession of 200 plants of Flowering Chinese Cabbage by randomly sampling. The number of polymorphic loci, the percentage of polymorphic loci, the genetic diversity index and the number of lack loci of different populations were analysed and calculated with RAPD technique. The results indicated that a sample of more than 30 plants could represent the genetic characteristics of a population of 200 plants. Based on the principle that the size of propagating population should double the size of effective one in germplasm regeneration, a sample of no less than 60 plants should be appropriate for regenerating Fowering Chinese Cabbage germplasm.