The invention relates to the field of electrochemical immunodetection, and especially relates to an ionic liquid-graphene nanocomposite, a preparation method and an electrochemical immunodetection method thereof. According to the immunodetection method, through using a double-antibody sandwich method, an apurinic/apyrimidinic endonuclease/redox factor antibody (anti-APE1) fixedly carried on the surface of an electrode carries out immunoreaction with an apurinic/apyrimidinic endonuclease/redox factor (APE1) in a sample solution, and is then combined with a room-temperature ionic liquid-graphene nanocomposite and an anti-APE1 co-coupling object marked by alkaline phosphatase (ALP) and ferrocene (Fc). Based on the electrochemical activities of the ALP-Fc-anti-APE and the room-temperature ionic liquid-graphene nanocomposite, a CV (cyclic vohammetry) catalytic current value is measured, and then the concentration of the APE1 in a detection sample is detected. The linear response range of the electrochemical immunodetection method provided by the invention is 0.1-80 pg/mL, and the lower detection limit is 0.04 pg/mL, therefore, the electrochemical immunodetection method is good in specificity and high in sensitivity.