An ultra-sensitive electrochemical sensor for detection of ascorbic acid（AA)was constructed by drop casting method with electrochemical sensing interface.Multi-walled carbon nanotubes （MWCNTs) and graphene oxide（GO) preventing the aggregation of MWCNTs were first added to the surface of glassy carbon electrode（GCE) to form a film.Subsequently,gold platinum core-shell nanoparticles（Au@Pt NPs) were immobilized on the surface of GO/MWCNTs/GCE through layer by layer assembly,forming a GO/MWCNTs/Au@Pt NPs/GCE 3D composite film.The as prepared electrode was used in the electrochemical detection of AA in phosphate buffer solution by differential pulse voltammetry（DPV) with a wide linear range and very low detection limit.There were good linear relationships between the redox peak current and AA in ranges of 0.005-0.5 μmol/L and 0.5-1 000 μmol/L,respectively,with their correlation coefficients of 0.999 and their detection limits（S/N=3) of 4.0×10-9 mol/L.The recoveries for the real human serum sample at three spiked levels of 0.01,0.1 and 10 μmol/L were in the range of 90.9%-108%,with the relative standard deviations（RSD,n=3)of 1.2%-2.8%.With a good selectivity toward AA,the sensor could effectively eliminate any interferences from small biological molecules such as dopamine,uric acid and glucose,etc.Therefore,the sensor is simple,efficient and sensitive,and could be widely used in clinical detection.