The invention discloses a preparation method of a 
formaldehyde adsorbent, and belongs to the technical field of adsorbing materials. According to the preparation method, Tofu is taken as a 
raw material; natural mildewing of Tofu is realized, and then mildewed Tofu is mixed with 
fresh milk for 
fermentation; under the action of 
mucor, proteins in Tofu and milk are degraded into amino acids; diatomite is taken as a 
raw material, 
citric acid is adopted for 
impurity removing so as to increase the specific surface area and the 
porosity of diatomite; diatomite is loaded with 
guanidine sulfamate via 
acylation and esterification of 
guanidine sulfamate, so that crosslinking reaction of 
guanidine groups and hydroxy groups with 
formaldehyde is realized, bridged bonds are formed, and immobilization of 
formaldehyde is realized; and at last, modified diatomite and amino acids are subjected to immersion together so as to load diatomite with the amino acids via adsorption, reaction of amino groups and guanidine groups in the amino acids with formaldehyde is realized so as to form 
hydroxymethyl derivatives, and removing of formaldehyde is realized. The formaldehyde adsorbent possesses excellent 
adsorption effect; 
indoor air secondary 
pollution is avoided; service life is long; and the formaldehyde adsorbent is worthy of popularization and application.