Effect and benefits of a product or service could be analyzed and evaluated by life cycle assessment during the whole life cycle. Urban sewage treatment plants could improve and control urban water pollution escalating, but it also had certain harm to environment. Effect and benefits of urban wastewater treatment plant A and B were analyzed and evaluated, 13 factors were selected, and comprehensive benefits were researched quantificationally using the method of analytic hierarchy process. It found that urban wastewater treatment plant A who applied A/O process had better benefits than urban wa...