The invention provides a reactive power compensation system and method for a motor group. The system comprises a plurality of asynchronous motors and a reactive power compensation device connected inparallel with the plurality of asynchronous motors; the reactive power compensation device comprises a plurality of parallel reactive power compensation units, and each reactive power compensation unit comprises a set of capacitor and a switch connected with the capacitor; the plurality of capacitors correspond to the plurality of asynchronous motors one by one, and the switch connected with eachcapacitor and a main switch connected with the asynchronous motor corresponding to the capacitor constitute a pair of linkage switches with the same action; and when one main switch is turned on and the switch linked with the main switch is turned on, the capacitor connected with the switch provides reactive power compensation for the asynchronous motor connected with the main switch. The system is simple in structure, simple and efficient in operation and easy to maintain and manage, and can effectively avoid resonance.