The invention discloses a corn stalk compound substrate suitable for soilless culture of vegetables and a preparation method thereof. The compound substrate comprises 8 volume parts of corn stalks and 2 volume parts of river sand. Various indexes of the compound substrate disclosed by the invention meet requirements on growth and development of the vegetables and reach a standard of soilless culture substrates; organic components account for about 80%, the service life reaches 2-5 years or longer, and the cost of the corn stalk compound substrate is reduced by 60-80% compared with that of conventional substrates, for example, 80% compared with that of rock wool, 75% compared with that of vermiculite, 75% compared with that of cocoanut shells, 70% compared with that of grass carbon, and 60% compared with that of perlite. The corn stalk compound substrate achieves recycling of stalks, saves natural resources, and provides an effective development outlet for protection of ecological environments.