Pressure control method and device of air conditioning system and air conditioning system

The invention discloses a pressure control method and device of an air conditioning system and the air conditioning system, and relates to the field of pressure control. By obtaining the current rotating speed of a compressor and obtaining the current evaporation pressure and condensation pressure of the compressor, whether the condensation pressure is larger than the preset maximum condensation pressure corresponding to the current rotating speed of the compressor or not is judged; if yes, the rotating speed of an outer fan of the air conditioner system is controlled to be increased, if not, whether the ratio of the condensation pressure to the evaporation pressure is within the preset pressure ratio range or not is further judged, if yes, it is judged that the pressure of the air conditioner system is normal, and if not, the rotating speed of the outer fan of the air conditioner is adjusted. By judging whether the condensation pressure is too large or not and judging whether the ratio of the condensation pr