For asymmetric optical fiber differential protection（AOFDP） with electronic transformer in one side and traditional transformer in the other side， configuration of optical fiber differential protection（OFDP） and sampling synchronization involved are overviewed briefly. The current synchronization solutions of OFDP in smart substation are then summarily introduced. Furthermore， with 500 kV Changshunan smart substation integrated test project， a synchronization test system is built for 220 kV line AOFDP. A method of current sampling synchronization test on both sides is proposed and reasons for production of differential current are also analyzed. Test results show that with channel delay compensation on both sides sampling sections， AOFDP may coordinate well， which meets project requirements.