The invention discloses a preparation method of 1,1-diphenylethylene shown in a formula (V). The method comprises the steps of firstly carrying out reaction on bromobenzene and magnesium chips in anhydrous 2-methyltetrahydrofuran to obtain a phenylmagnesium bromide Grignard reagent, and then dripping acetophenone into the phenylmagnesium bromide Grignard reagent to react, so as to generate 1,1-diphenylethanol; finally, dewatering 1,1-diphenylethanol in the presence of a sulfoacid functional ionic liquid catalyst, so as to obtain 1,1-diphenylethylene shown in the formula (V). The preparation method disclosed by the invention is short in reaction step, mild in condition, simple and convenient to operate, high in product yield, low in production cost, friendly to environment, and applicable to industrial production.