The invention discloses a heavy metal adsorbent used in sewage treatment and application of the heavy metal adsorbent. According to the characteristics of heavy metal wastewater, proper plant waste, such as straws, barks and sawdust, is selected for optimal combination with a chemical adsorbent and a microbial agent; firstly, a large amount of cellulose contained in the straws, the barks and the sawdust can be separated out under the action of other chemical agents; by virtue of the auxiliary coordination effect of the chemical adsorbent, all microorganisms generate available substances in a growth process of the microorganisms and secreta of the microorganisms form matrixes and raw materials which grow mutually; furthermore, due to a mutualism and multiplication relation, a complicated, stable-structure and multifunctional microorganism community with various germs is formed; mutual benefits are achieved in a heavy metal-containing wastewater purification process, and the maximum united advantage is given full play; the heavy metal adsorbent is good in treatment effect, low in cost and outstanding in economical benefit, and the wastewater is discharged after meeting a standard.