Abstract: Companion with potato onion can suppress tomato root-knot nematode disease.However,whether flavonoids in potato onion bulb could inhibit tomato root-knot nematode disease remains unclear.In this study,the contents of flavonoids （rutin,myricetin,kaempferol,quercetin and the total flavonoids） from 44 potato onion bulbs and their effects on tomato root-knot mortality,egg hatching inhibition rate and Cf value of chemotaxis were investigated.Moreover,the correlations between flavonoids and root-knot nematode incidence rate,disease index,soil insect control effect and root-knot index were also assessed.The results found that the contents of flavonoids from 44 potato onion bulbs were ranged from 593.22 to 2 204.88 mg·100 g^-1DW.Among them,the contents of flaconoids were higher in M11 and M51 mainly with quercetin as the main compounds,and the values are 2 186.59 and2 204.88 mg·100 g^-1DW,respectively.The contents of myricetin,quercetin,kaempferol and tota flavonoids in potato onion bulbs were significantly positively correlated with the egg hatching inhibition rate of root-knot nematode,and the content of flavonoids were significantly negatively correlated with the Cf value of root-knot nematode chemotaxis.In addition,myricetin was significantly positively correlated with soil insect control effect,and significantly negatively correlated with disease index and root-knot index of tomato root-knot nematode.Quercetin was significantly negatively correlated with tomato root knot index,root knot nematode disease index and incidence.Overall,companion with potato-onion can reduce root-knot nematode of tomato,which closely related to the contents of flavonoids in potato onion.