The invention discloses a method for preparing modified soybean straw pig fodder and the pig fodder prepared by means of the method. The method comprises the following steps that 1, soybean straw, soybean hulls, soybean meal, soybean oil and soybean bran are placed in an ultrafine crusher to be crushed into fine powder with the particle size of 500-600 mesh; 2, a modifier is added to the fine powder in the step 1, wherein the modifier is prepared from, by weight, yeast, ceriporiopsis subvermispora, phanerochaete chrysosporium, variegated coriolus versicolor, pleurotus ostreatus, hirschioporuslacteus and coriolopsis gallica; a mixture is formed after the addition of the modifier and poured into a fermentation tank, water is added for stirring, and the moisture content of the mixture is controlled within 15%-30%; 3, after the water is added for stirring and the temperature rises to 30-40 DEG C, and fermentation is conducted for 12-20 hours; 4, the fermented material in the step 3 is taken out and placed in a granulation dryer for drying granulation, and the finished pig fodder is obtained after the granulation is completed.