The invention relates to a preparing method of lowering residual monomer content of ultra high molecular weight anion-type polyacrylamide. The invention has the technical scheme as follows: acrylamide (AM), 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and acrylic acid (AA) are taken as a synthetic monomer; a kettle-type chunk polymerization technology, a complex initiation system, hydrolyzerposthydrolysis and fluidized bed drying preparation are adopted; acrylamide dry powder is white power-type particle; polyacrylamide colloidal particles in a hydrolyzer are transmitted to a static fluidized bed for drying after pelleting by a secondary pelletizer, are crushed by a grinder and are packaged into bags. The invention has the beneficial effect that the content of a residual monomer is controlled below 0.05%, which can satisfy the technical requirements of three-time adoption, sewage treatment and raw water treatment.