The invention relates to a method for producing ferrous sulphate monohydrate, which belongs to the field of chemical industry. The technical problem solved in the invention is to provide the method for producing the ferrous sulphate monohydrate, and the purity of the ferrous sulphate monohydrate produced by using the method can be more than 99 percent. The method comprises the following steps: a,taking ferrous sulfate heptahydrate (by-products produced in the process of producing titanium dioxide through a sulfuric acid process) as raw material, heating the ferrous sulfate heptahydrate to 60to 80 DEG C, then adding reaction amounts of barium chlorides, irons and organic flocculants into the ferrous sulfate heptahydrate; b, continuing to heat up the obtained mixture so as to cause the mixture to boil, then standing for 1h to 4h; and c, separating and then heating the liquid supernatant until the liquid supernatant is boiling, then filtrating the liquid supernatant when the liquid supernatant is still hot to obtain a filter cake, drying the filter cake so as to obtain the ferrous sulphate monohydrate.