The invention discloses a unit control method, device and system, wherein the unit control method includes: acquiring working parameters of a unit; judging whether coolant injection quantity of the unit is abnormal according to the working parameters; if yes, correspondingly adjusting compressor operation frequency and/or fan frequency according to the abnormal state of the coolant injection quantity. The unit control method, device and system have the advantages that when the coolant injection quantity of the unit is abnormal, namely the requirement of the unit is not met, compressor operation frequency and/or fan frequency can be adjusted to change coolant circulation quantity of the unit; the coolant circulation quantity of a system is closely linked with stable operation of a unit, andtherefore, the unit can operate stably, can gain higher energy efficiency and can be protected; unit stopping due to frequency triggering of a failure protection mode can be avoided.