Abstract: Based on experiment between occurrence of black-streaked dwarf viral disedse of hybrid rice (RBSDV) and its economic threshold in 1998~2003. The results showed that incidence of RBSDV was tested during different hybridized combination and growth stage of hybrid rice, and infection probability in seeding stage and vegetative stage on hybrid rice ,and relationship of incidence of last stubble (m%) and next stubble(M%) and yiled loss rate(Y%) were analysed, the model are as follows M=1.6822m+0.1049 and Y=0.9776M-0.1935 .Relationship of various small brown planthopper(SBPH) (Laodelphax striatellus) population density(X) and infection rate and yiled loss rate (Y%) was invesligated , the model are as follows Y1=12.1841X1-1.0784 in seeding stage and Y2=4.5159X2-0.4620 in the early days of field stage .It was provided that control optimal time were 2 nd ~5th leave age in seeding stage and early tillering stage in the field stage. On economical injuring level the economic threshold was determined as the diseased rate reaching 1.0% last stubble and 0.15 viruliferous SBPH vector /0.11m2 in seeding stage and 4000viruliferous SBPH vector /667m2 (20 viruliferous SBPH vector/100 clusters) in early tillering stage on hybrid rice.