The invention discloses a new method for producing exterior sodium dick acid anhydride, belonging to the synthesis field of organic chemistry. In the method, maleic anhydride and mixed carbon five are taken as raw materials. The method comprises the steps of: directly absorbing cyclopentadiene by maleic anhydride at 0-5 DEG C to react so as to generate interior sodium dick acid anhydride; and taking the interior sodium dick acid anhydride as a raw material, taking short chain alcohol as solvent, and taking urotropin, benzoyl peroxide and (Cu (dppm) (NO3)) 2 as catalyst to synthesize the exterior sodium dick acid anhydride. Compared with the prior art, in the method, a low-price ethane byproduct and the mixed carbon five are taken as the raw material to prepare the exterior sodium dick acid anhydride, so that the yield is obviously higher than the conventional technology and reaches more than 96%, and the solvent pollution is reduced; and therefore, the method is more suitable for the industrial production.