The invention discloses a selfheal dreg floatation seedling substrate and a preparation method thereof. The selfheal dreg floatation seedling substrate comprises 1 part of fermentative selfheal dreg, 0.5-1 part of earthworm excrement, 0-0.5 part of turf and 0.5-1 part of vermiculite. The preparation method is wide in the selection of raw materials, easy and convenient to operate and simple in process; the situation that the selection of the traditional substrate depends on non-renewable resources including perlite, vermiculite and the like is changed; the selected raw material is selfheal dreg abandoned by pharmaceutical factories, the seedling substrate is light in tactile sensation, and the porosity, volume weight and proportion of the substrate approximate to those of the turf, as a result, the pollution of the dreg to the environment can be solved, meanwhile, the waste dreg can be reused, and further the effects on environmental protection, energy economization and improvement of the utilization efficiency of humic acid are realized; the dreg is utilized as the main raw material of the seedling substrate, and the raw material is industrial waste residue, so that the cost is low, the preparation process is simple, and popularization and application are facilitated; the emergence rate of cabbages cultivated by utilizing the substrate can reach over 90 percent, the degree of uniformity of seedlings is high, the index of strong seedlings is also high, the growth is good and the cost is lowered.