According to the special properties of functionalized ionic liquid modified graphene （IL-GR） and nano Au,IL-GR was firstly immobilized on the glass carbon electrode via chitosan （CHIT） cross linking,and then a layer of nano Au was adsorbed to form Au/IL-GR-CHIT composite film.Finally,acetylcholinesterase（AChE） was immobilized on the composite film by adsorption.A novel biosensor for detection of organophosphorus pesticides enzyme was developed,and used for the determination of trichlorfon.Different technologies were employed to study the construction process and the electrochemical properties of the biosensor.The results showed that the nanocomposite not only provided a biocompatible microenvironment to keep the bioactivity of AChE,but also exhibited a strong synergetic effect improving the sensing properties of biosensor.Linear relationship between inhibition percentage（A） and logarithm of concentration of trichlorfon was found in the range of 2.0×10-10 -1.0×10-6 mol/L,and the detection limit（S/N=3） was calculated to be 2.1×10-12 mol/L.The recoveries of trichlorfon in vegetable ranged from 97.5% to 107.2%.