The invention provides a third-order nonlinear optical material, namely a tetrabutyl ammonium fullerene ball and a synthesizing method thereof, which belongs to the field of functional materials. The prior inorganic and organic nonlinear optical materials have the problems of easy deliquescence, poor thermal stability, complicated preparation and the like respectively. The molecular formula of the tetrabutyl ammonium fullerene ball provided by the invention is (NH4)18[(C16H36N)4]24[Mo132O372(H2O)72(CH3COO)30].ca.7NH4CH3COO.ca.173H2O. In the method, after {Mo132} and tetrabutyl ammonium bromide are dissolved in water respectively according to the mass ratio of 1 to 42, and are adjusted by acetic acid respectively until the pH value is between 3.5 and 4.5, the {Mo132} and the tetrabutyl ammonium bromide are mixed to obtain the tetrabutyl ammonium fullerene ball. The third-order nonlinear optical material has the advantages of uneasy deliquescence, high thermal stability, larger nonlinear absorption and non-linear refraction coefficient, self-defocusing property and simple preparation.