The invention provides a safety protection method and system of an air conditioner, which are suitable for the air conditioner adopting a combustible refrigerant. The air conditioner comprises an indoor unit and an outdoor unit. The safety protection method comprises the following steps: detecting the concentration of the refrigerant leaked into the indoor unit and/or leaked into the outdoor unit; judging whether the concentration of the refrigerant leaked into the indoor unit and/or leaked into the outdoor unit exceeds a first pre-set concentration value or not; when judging that the concentration of the refrigerant leaked into the indoor unit and/or leaked into the outdoor unit exceeds the first pre-set concentration value, releasing inert gas into the indoor unit and/or the outdoor unit, and closing a gas pipeline and a liquid pipeline between the indoor unit and the outdoor unit; and controlling the compressor of the air conditioner to be stopped. According to the technical scheme, when the combustible refrigerant in the indoor unit and/or the outdoor unit leaks, the possibility of ignition and explosion is effectively avoided and the safety of the air conditioner which utilize the combustible refrigerant is improved.