The present disclosure provides a defrosting method for an air conditioner. The method includes: acquiring outdoor temperature and outdoor humidity if the air conditioner enters a defrosting mode; judging whether the outdoor temperature and the outdoor humidity satisfy a predetermined condition; and controlling an outdoor fan to rotate reversely according to tube temperature of an outdoor heat exchanger and a defrosting period, so as to defrost a protecting housing surrounding the outdoor heat exchanger if it is judged that the outdoor temperature and the outdoor humidity satisfy the predetermined condition. The defrosting method may efficiently defrost the protecting housing surrounding the outdoor heat exchanger completely. The present disclosure further provides a defrosting device for an air conditioner.