A refrigeration system and refrigeration method for a data center are disclosed. The refrigeration system includes: a first heat exchanger disposed on a back plate of an indoor cabinet of the data center, and a phase-change heat-exchange cooling tower disposed outdoor of the data center. The first heat exchanger and the phase-change heat-exchange cooling tower are communicated by a secondary refrigerant delivery pipeline. The phase-change heat-exchange cooling tower transfers heat carried in the secondary refrigerant into air and condenses the secondary refrigerant to a liquid again; the secondary refrigerant employs a phase-change heat-exchange working medium. An air pump is disposed in the phase-change heat-exchange cooling tower and on a by-pass of the secondary refrigerant delivery pipeline to pressurize the secondary refrigerant in gas-state delivered in the secondary refrigerant delivery pipeline to increase the condensing pressure for condensing the secondary refrigerant to a liquid again.