The invention relates to a single-refrigerant loop and multiple-suction pressure steam compression refrigeration/heat pump system. The system comprises a condenser, evaporators, compressors, throttling devices, heat release working medium connecting pipes and refrigerant connecting pipes. The condenser, the throttling devices, refrigerant channels of the evaporators and the compressors are connected into a circulation loop through the refrigerant connecting pipes, and a refrigerant flows circularly in different forms in the circulation loop. The heat release working medium connecting pipes are connected with heat release working medium channels of the evaporators, and heat release working media are cooled through the evaporators. The evaporators adapt to multiple evaporation pressures, the compressors adapt to multiple suction pressures, and the number of the evaporation pressures which the evaporators adapt to is equal to that of the suction pressures which the compressors adapt to. The number of the arranged throttling devices is equal to that of the evaporation pressures and that of the suction pressures. Compared with the prior art, the multiple suction pressures are achieved in a single-loop refrigerating system, so that the power consumption of the compressors is reduced, and accordingly the efficiency of the steam compression refrigeration/heat pump system is improved.