PURPOSE: An environment-friendly sludge treating agent, a producing method thereof, and a sludge treating method using thereof are provided to use seashells, gluten, chaff materials, bentonite, and zeolite for treating sludge inside a dredged sediment of a reservoir. CONSTITUTION: A producing method of an environment-friendly sludge treating agent comprises the following steps: preparing 18~34wt% of seashell powder plasticized at 900~1,200deg C, 18~34wt% of gluten powder heated at 60~100deg C, 32~55wt% of chaff material powder, 0.05~3wt% of bentonite powder, and 1~5wt% of zeolite powder(S10, S20, S30); and mixing all the prepared materials(S40).