The invention is applicable to the field of refrigeration equipment control, and particularly relates to an air conditioner capacity regulating and controlling method and system. According to the method and system, a user preset temperature digital voltage signal, an outdoor heat exchanger return air temperature digital voltage signal and an indoor heat exchanger return air temperature digital voltage signal are correspondingly generated according to a user preset temperature value, an outdoor heat exchanger return air temperature value and an indoor heat exchanger return air temperature value, a corresponding start-stop time ratio of an outer fan of an air conditioner is acquired to control stop and start of the outer fan of the air conditioner, and further corresponding start and stop control is performed on the outer fan of the air conditioner under different environmental temperature conditions so as to regulate capacity output of the air conditioner, so that an indoor heat exchanger of the air conditioner is prevented from frosting during refrigeration in low-temperature environment, refrigeration effect is improved, and a compressor is ensured not to be damaged in normal operation so as to prolong service life thereof.