The invention relates to a system and a method of preparing hydrogen rich gas and carbon monoxide from synthesis gas. The system mainly comprises a synthesis gas purifying unit, a low-temperature liquefying separation unit and a CO product compressor, wherein the low-temperature liquefying separation unit is composed of a first plate-fin heat exchanger, a second plate-fin heat exchanger, a flash separator, a high-pressure rectification tower and a low-pressure rectification tower; a first evaporator is arranged at the bottom of the high-pressure rectification tower; a second evaporator is arranged at the bottom of the low-pressure rectification tower; and a first condenser is arranged at the top part of the low-pressure rectification tower. The system and the method are strong in adaptability to raw gas, little in equipment and small in investment, lower the requirement for impurities of the synthesis gas, eliminate a nitrogen compressor and an expander, increase the hydrogen recovery rate of a device and reduce the processing load of PSA or a membrane separation system.