The invention relates to the field of agricultural planting and vegetable planting, and particularly relates to a specific soybean straw nursery substrate for vegetables and its preparation method. An ideal soybean straw nursery substrate is prepared by using agricultural waste soybean straw as a main raw material of a vegetable nursery substrate, researching soybean straw biological maturity, optimized substrate mixture ratio, regulation of physical and chemical parameters and influence of various substrate formulas on the growth and development of vegetable seedlings, and combining with the preparation method and condition screening. The soybean straw nursery substrate is simple in composition, safe in use, low in production cost, simple and easy-practice in processing technique, and good for popularizing and applying to the vegetable planting field; thus the specific soybean straw nursery substrate for vegetables and provides a new way for the comprehensive use of the soybean straw resource.