The invention relates to a container seedling substrate suitable for citrus growth. The seedling substrate is composed of sludge and river sand. The sludge is one or more selected from water supply sludge, industrial wastewater sludge, and domestic sewage sludge. According to the container seedling substrate, the sewage sludge is adopted as a raw material, such that waste sewage sludge can be utilized, and a problem of sludge disposal difficulty can be solved. Also, the use of a traditional substrate raw material peat can be reduced, such that cost can be reduced, and the non-renewable resource can be reasonably protected. Also, the raw material cost is low. With the organic seedling substrate, cultured citrus seedling survival rate can reach 100%. With the container seedling substrate provided by the invention, a nutrient release speed can be comprehensively reduced, nutrient loss can be reduced, and sustained-release and long-effect effects can be achieved. With the substrate, one-time fertilizer can be adopted, and multiple times of fertilizer addition during a seedling growth process is not needed. Cost is reduced, and operation is reduced. With the substrate, citrus seedling growth condition is good, seedling emergence is uniform, and cost is low. The substrate and the method are novel technologies that can be popularized.