The present application provides a centrifugal compressor for a refrigeration system and a refrigeration system. The centrifugal compressor has a reverse braking function and comprises: a rotor shaft; a compressor impeller connected to the rotor shaft; a brake component on the rotor shaft, wherein a periphery of the brake component is made of magnetic conductive material; a plurality of sets of electromagnets fixedly arranged at radial outward of the brake component; a sensor device for sensing a rotational speed and direction of the rotor shaft; and a controller connected to the sensor device, wherein the controller receives signals from the sensor device and supplies power to the plurality of sets of electromagnets based on the signals. The centrifugal compressor and refrigeration system according to the various embodiments effectively suppress the reverse rotation of the compressor rotor shaft caused by the reverse airflow during unexpected shutdown.