The present invention discloses a retractable side protecting airbag for a child safety seat which includes a side protecting base provided on an outer side surface of the seat body. Specifically, the side protecting base is provided with the retractable side protecting airbag. The retractable side protecting airbag is correspondingly provided with an air deflating hole. The side protecting airbag is internally provided with a resetting structure. An outer end of the retractable side protecting airbag is provided with a side protecting cover. The protecting cover and the side protecting base are locked to each other and work collaboratively for folding the retractable side protecting airbag. The present invention has a reasonable structure and a long distance for crumpling, and is capable of providing buffering and effective energy absorption, thereby greatly reducing the damage to children from side crashes.