The invention provides a preparation method of 
straw-based magnetic 
charcoal. The method includes the following steps that (1) 
straw is cleaned, naturally air-dried, dried in a 
drying oven, smashed and sieved, and 
straw powder is obtained; (2) the straw 
powder is pre-carbonized in a 
muffle furnace, washed and dried, and a straw-based pre-carbonized product is obtained; (3) the straw-based pre-carbonized product is put in a 
tube furnace, 
argon is fed, 
pyrolysis is performed at the temperature of 400-500 DEG C for 2-3 hours, cooling is performed till the temperature reaches the 
room temperature,washing is performed till the product is neutral, 
drying and 
grinding are performed, then sieving is performed, and straw-based 
charcoal is obtained; and (4) the straw-based 
charcoal and 
oleylamine are put in a reaction kettle for uniform mixing and 
ultrasound treatment, 
ferric acetylacetonate is added into a 
mixed solution, the 
mixed solution is stirred uniformly, a 
liquid product is obtained, ablack substance is separated out after 
centrifugation is finished, and the straw-based magnetic charcoal is obtained. Compared with original charcoal, the prepared straw-based magnetic charcoal has the advantages of being better in 
thermal stability and larger in specific surface area, and medium and large pores in the pore structure of the straw-based magnetic charcoal prevail.