The invention provides a control method and control system for an air conditioner, and the air conditioner. The control method for the air conditioner comprises the steps that when a compressor operates in a preset frequency rising mode, whether the cold air preventing mode of an indoor unit is ended or nor is judged in real time; when the cold air preventing mode is ended, the compressor is controlled to operate at the current frequency, and whether the compressor meet the condition for quitting the current frequency operating mode or not is judged in real time; when the compressor meets the condition for quitting the current frequency operating mode, the compressor is controlled to continue to operate in the preset frequency rising mode; and when the compressor does not meet the condition for quitting the current frequency operating mode, the compressor continues to be controlled to operate at the current frequency. According to the control method for the air conditioner, soft starting of an air-conditioning system is ensured, the phenomenon of liquid impact caused by instant liquid returning of the compressor is avoided, the compressor can operate more stably in the frequency rising process, the reliability of the compressor is improved accordingly, abrasion of the compressor is reduced, and the service life of the compressor is prolonged.