Abstract: This paper studies the phenotype characteristics and mechanism of formation of WaR84h 89b10,eye-variegation strain of Drosophila melanogaster.The study shows the essential characteristics of position effect,that is,chromosome recombination,thermo-reaction and gene expression that is related to the sepation position of heterochromation.In addition to that,the study also shows that 89b10 is the regulator gene-W,which is between 4 and 5 down the gene-W.The newly found regulator gene is named R(W)W.The formation of the phenotype of the eye-variegation is due to the augmentation of a protein involved in the heterochromotion at the separation of In(1)4D,5B,which causes the inactivation of the gene-R(W)W nearby,therefore,this irregular expression leads to the irregular expression of gene-W.