Abstract: Wilfordine and wilforine with contact toxicity against some larvae of insect,were isolated from the insecticidal plants of Tripterygium hypoglaucum. For investigating their insecticidal mechanism,their poisoning symptoms were observed when wilfordine and wilforine were applied on the pronoturm of Mythimna separata by topical application. The results showed that the larvae were narcotized after 2 hours,revived completely after 8 hours,then narcotized again after 24 hours,part of the larvae were dead after 48 hours. The results also showed that the medium narcosis dose (ND50) of wilfordine and wilforine were 8.82 μg/larva,4.58 μg/larvae against the 3rd instar larvae of M. separata respectively.The ND50 of wilfordine and wilforine were 4.71 μg/larva,3.46 μg/larva against the 3rd instar larvae Plutella xylostella respectively. In vitro and in vivo,the effects of wilfordine and wilforine on Na+ -K+ -ATPase from the head of the 5th instar larvae of M.separata were investigated . The results showed that the Na+-K+-ATPase in the central nervous system was inhibited by wilfordine and wilforine,and the inhibition rate was dependant on the concentration. It suggested that Na+-K+-ATPase may be an acting target of wilfordine and wilforine against some larvae of insect.