Abstract: Distribution of imidacloprid in walnut tissues after trunk injection was examined by high performance liquid chromatography (HPLC).The results showed that imidacloprid could be transmitted and distributed in different walnut tissues after application.The concentrations of imidacloprid,which differ in various tissues,varied from high to low in leaves,walnut hull and walnut kernel.The residue of imidacloprid remained a long period in walnut tissues after injection.The concentrations of imidacloprid in leaves,walnut hull and walnut kernel were 0.256,0.178 and 0.046 mg/kg at 60 days after injection,and all were bellow 0.05 mg/kg at 80 days after trunk injection.It is suggested that when imidacloprid through trunk injection is applied to control walnut pest,the period between application time and harvesting time should be kept larger than 60 days.