The invention discloses a liquid ethane conveying pipeline pressure protection system and method. The system comprises forward pressure relief systems and reverse pressure relief systems which are arranged in parallel on trunk line pumps or valve bypasses. According to the system and the method, the pump or valve front pressure increment caused by action of the pumps or trunk line valves in a liquid ethane pipeline or the isolation section pressure increment caused by temperature rise is automatically released into adjacent upstream and downstream trunk lines by stimulating relief devices arranged on the pumps of the valve bypassed so as to prevent overpressure mediums from entering the atmosphere and limit the highest operating pressure of each pipe section. The system and the method havethe advantages that the water hammer overpressure problem under transient operation of a pipeline can be solved, the influence on the strength of the pipeline due to the volume change caused by influence of the temperature of the mediums after shutdown of the pipeline can be avoided, the overpressure mediums are not discharged from the system after being released, and therefore the investment ofaccessory facilities are reduced, and the safety, environmental protection and energy conservation effects can be achieved.