A device for preventing cold air during heating on an air conditioner, comprising: a temperature detecting element, configured to detect, after heating is started, an indoor ambient temperature and an outdoor ambient temperature respectively to determine a general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located; a first determining element, configured to, determine whether an evaporator inner-tube temperature satisfies an evaporator inner-tube temperature condition required for entering a cold air prevention mode corresponding to the general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located, or determine whether a duration, for which a compressor and a four-way valve operate, reaches an operating duration of the compressor and the four-way valve, required for entering the cold air prevention mode corresponding to the general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located, or determine whether a current intensity continuously reaches a first preset current intensity threshold for a predetermined duration; a first controlling element, configured to start, when any one determining result of the first determining element is yes, an inner blower fan at a first preset wind speed; a second determining element, configured to determine, after the inner blower fan is started, whether the evaporator inner-tube temperature satisfies the evaporator inner-tube temperature condition required for exiting the cold air prevention mode corresponding to the general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located, or determine whether the current intensity continuously reaches a second preset current intensity threshold for a predetermined duration, or determine whether a duration, for which the inner blower fan operates at the first preset wind speed, reaches a first preset duration; and a second controlling element, configured to switch, when any one determining result of the second determining element is yes, the inner blower fan to operate at a second preset wind speed, the first preset wind speed being smaller than the second preset wind speed. a temperature detecting element, configured to detect, after heating is started, an indoor ambient temperature and an outdoor ambient temperature respectively to determine a general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located; a first determining element, configured to, determine whether an evaporator inner-tube temperature satisfies an evaporator inner-tube temperature condition required for entering a cold air prevention mode corresponding to the general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located, or determine whether a duration, for which a compressor and a four-way valve operate, reaches an operating duration of the compressor and the four-way valve, required for entering the cold air prevention mode corresponding to the general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located, or determine whether a current intensity continuously reaches a first preset current intensity threshold for a predetermined duration; a first controlling element, configured to start, when any one determining result of the first determining element is yes, an inner blower fan at a first preset wind speed; a second determining element, configured to determine, after the inner blower fan is started, whether the evaporator inner-tube temperature satisfies the evaporator inner-tube temperature condition required for exiting the cold air prevention mode corresponding to the general temperature range within which the indoor ambient temperature and the outdoor ambient temperature are located, or determine whether the current intensity continuously reaches a second preset current intensity threshold for a predetermined duration, or determine whether a duration, for which the inner blower fan operates at the first preset wind speed, reaches a first preset duration; and a second controlling element, configured to switch, when any one determining result of the second determining element is yes, the inner blower fan to operate at a second preset wind speed, the first preset wind speed being smaller than the second preset wind speed.