Natural gas expansion compressor is the key equipment of natural gas terminal expansion refrigeration process， which plays a vital role in the recovery rate of natural gas byproducts. At present， all natural gas processing terminals use imported expansion compressor sets， but the imported compressor sets have large investment and high maintenance and spare parts costs in the later stage due to technical constraints. Two imported expansion compressors (1.2 million cubic meters/day) that have been used for many years and have frequent failures have been reformed domestically in a onshore terminal of Bohai oil and gas field. The localization transformation of expansion compressor rotor assembly mainly includes expansion end impeller， compression end impeller， main shaft， bearing， diaphragm shaft seal， connecting key and other auxiliary parts. For the first time， the rotor assembly of the imported expansion compressor of natural gas onshore terminal in Bohai area was localized， and the spare parts of the unit did not depend on imports， which was completely independently developed and produced in China. The supply channels were smooth， and the required maintenance spare parts could be purchased in the shortest time， and the technical core parameters were controlled to shorten the maintenance cycle， saving the later maintenance time and cost. The comparison results show that the field application effect of domestic unit parts is good， the unit has been running continuously for 78，840 hours without abnormality， and its performance far exceeds the service life of imported parts， which provides a good reference for similar projects of natural gas expansion refrigeration.