The invention provides a collapsible baby diaper changing bench capable of easily adjusting retainer belts extending inside the bench. The collapsible baby diaper changing bench comprises: a pedestal; a changing bench main body disposed on the pedestal and rotating relative to the pedestal through a rotation shaft; and an infant putting mat disposed on the changing bench main body. The infant putting mat is positioned by a pair of the retainer belts on the changing bench main body. One of the retainer belts comprises a belt buckle inserting port and is penetrated by the other retainer belt. Belt buckles are installed on the top ends of the retainer belts. The retainer belts extend on the inner surface of the changing bench main body. Windows used for adjusting the retainer belts are formed in the changing bench main body.