The invention provides a preparation method for fumaric acid, and relates to the production technical field of fumaric acid. The preparation method comprises: adding maleic anhydride into a reaction medium, without any catalyst or adding sulfuric acid and phosphoric acid as catalysts, in an N2 sealed environment, heating to 140 DEG C-220 DEG C and stirring for a reaction, after the reaction is finished, stirring for cooling and crystallization until the temperature is 40 DEG C or less, centrifuging the crystallization liquid to obtain fumaric acid crystal, drying to obtain high-purity fumaric acid. The yield of fumaric acid by employing the preparation method reaches up to 99.5% or more, the mother liquor after the fumaric acid crystal liquid is centrifuged can be subsequently cycled as the reaction work medium, so that no any wastewater or exhaust gas is generated, and the green production of fumaric acid is realized. Fumaric acid prepared by employing the preparation method is accord with national standard of 'GB25546-2010 foodstuff additive fumaric acid' and 'NY-T920-2004 feed grade fumaric acid'.