The invention relates to a plant growth-promoting microbial inoculum for tailing restoration, which is prepared by taking a plant growth-promoting functional flora as a main body and taking corn straw biochar serving as an adsorbent, polyvinyl alcohol serving as an embedding agent, sodium alginate and Ca (NO3)2 serving as a cross-linking agent for fixing. The member strains are complementary in function, high in diversity and consistent in growth rule, and mutual antagonism among the strains does not exist. The invention provides a preparation method of the plant growth-promoting microbial inoculum and an application of the plant growth-promoting microbial inoculum in strengthening phytoremediation of rare earth tailing soil. The microbial inoculum has multiple properties of fixing carbon, fixing nitrogen, dissolving phosphorus, supplying iron, retaining water, improving plant stress resistance, promoting plant growth and the like, and can remarkably improve the biomass, nutrient absorption, soil nutrients and the number of microorganisms of rare earth tailing plants. The microbial inoculum is applied in a granular form, is beneficial to storage and application, and is relatively high in practicability. The product has the characteristics of comprehensive performance, long-acting broad spectrum, simplicity, safety, easiness in storage and the like, and is suitable for multiple stress tailing environments such as soil acidification, water deficiency, nutrient depletion and heavy metal pollution.