It has been proved by many field experiments and QTL mapping results that among genes affecting some quantitative traits there are some major genes with larger genetic effect and some polygenes with smaller genetic effect. For such traits, the distribution of segregating population demonstrates multimodality, and this is the characteristic of the mixture of more than one distributions. Mixture distribution models have been used extensively as models in a wide variety of practical situations where data can be viewed as arising from two or more populations mixed in certain proportions. Akaike's Information Criterion(AIC) has been used to identify the existence of major genes affecting quantitative traits. Under the existence of major genes, the genetic effects of these genes and their genetic variance were estimated through segregation analysis. The genotype of major gene of F2 individuals of were determined by clustering using Bayesian criterion. With P1, P2, F1 and F2 populations, the likelihood ratio test was used to test the existence of polygenes. In the end, the inheritance of soybean flowering date is analyzed. One major gene was found in F2 population derived from Guludou x Shanghaihongmangzao.