Objective To study the effect of the genetic factors on the occurrence and development of type 2 diabetes mellitus(T2DM) and its general genetic pattern.Methods 21 T2DM cases,as proband,were investigated for T2DM genealogical tree.The heritability of T2DM was estimated by Falconer method.T2DM segregation rate and genetic pattern were evaluated with Penrose's method,Li-Mantel-Gart method and the threshold value model method of Jiang San-Duo.Results The prevalent rate of T2DM in first-degree relatives was 7.6%,which was higher than that in general population.The heritability of T2DM was 46.8%.The s/q score was 3.312 with Penrose's method,which was near to 1/q1/2.The segregation rate P was 0.131,which was lower than 0.25.The theoretical prevalent rate in first relatives was 8.0%,while the investigated prevalent rate was 7.6%.Conclusion There is an obvious heritable trend in T2DM.It is fit to the multi-factorial inheritance pattern but the mono-gene heritability model.