Abstract: In this paper , the sex-effects of the cocoon quality characters in silkworm was predicted with Mixed linear model ：The fact that the probability of effect variance and predictability of random gender of whole cocoon weight, cocoon shell weight, ratio of cocoon shell and pupa weight reached a level of extreme significance showed that the gender effect of the four traits was extremely significant, which matched with the reality completely. The predictive values of gender effect of the four traits of female(male) were 0.248g（-0.247g）、2.423cg(-2.394)cg、-1.976%(1.992%)和0.224g(-0.223g) respectively. Each trait showed single peak distribution after adjusting by sex-effects, which fitted for the request that quantitative traits should show continuously normal standard distribution if QTL analysis was taken.