The invention discloses an ionic liquid electrolyte and a preparation method and application thereof. The preparation method comprises the following steps of: preparing an intermediate chloride 1-allyl-3-methylimidazole by using allyl chloride and N-methylimidazole, removing impurities, and finally synthesizing hydrophobic ionic liquid by using the intermediate and bi(lithium trifluoromethyl sulfimide) subjected to impurity removal through a microwave reaction method. According to the defects in the prior art, the ionic liquid electrolyte is wide in electrochemical window, high in electrical conductivity and low in viscosity and can be used for a lithium ion battery.