The invention relates to the field of 
urban runoff biodegration, in particular to a planting soil for a rainwater-regulation permeable tree 
pool and a preparation method thereof. The planting soil includes, by weight, 70-80 parts of sandy 
loam, 20-30 parts of coco 
coir, 5-10 parts of flay ash and 0.5-1 part of 
humus. The preparation method includes the following steps that 1, 
raw material treatment is conducted, wherein in the sandy 
loam treatment, sandy 
loam is taken, broken up and then air cured for 1-2 days, and a sterilizing agent is sprayed for sterilization after air-curing; in the coco 
coir treatment, coco 
coir is taken, soaked in water to make the 
conductivity of the coco coir lower than 0.5 mS / cm and then air cured for 1-2 days after 
dewatering, the coco coir needs to be turned three-four times during air curing, and then a sterilizing agent is sprayed for sterilization; in the 
fly ash treatment, the 
fly ash is taken, dried until the 
water content reaches 5%-8% and ground until the particle size is 0.1-0.2 mm; 2, the raw materials are blended, wherein the 
humus is taken to uniformly mixed with the sandy loam, the coco coir and the 
fly ash treated in the step 1. The planting soil can ensure the 
normal growth of plants, the 
permeation effect is good, and the removal effect of runoff contaminants is good.