An air pump for an inflatable article has a housing, and a blower, a switch assembly, an air valve and a fan guard mounted in the housing. The switch assembly has a slider and a driving device sliding the slider and the air valve to switch operating modes of the air pump. Thus, the air pump inflates or deflates the inflatable article or maintains or fine-tunes the air pressure inside the inflatable article. Therefore, the first and second openings of the housing are disposed on the housing for connection to different kinds of inflatable articles and the airflow directly flows through the air pump so inflating and deflating the inflatable article is fast.