Under the background of COVID-19，city diplomacy still maintains an active momentum of exchanges. The main practices include：close mutual assistance between friendly cities，large-scale multilateral cooperation organized by the international city networks，international initiatives related to anti-epidemic work and recovery，and cultural and economic cooperation in the difficult situation. City diplomacy reveals the following characteristics：the consciousness of active participation，flexible form of practice，pragmatic orientation of external action，and values of second-track diplomacy. It also has some shortcomings，such as the lack of effects，the overlapping of mechanicm’s functions，imbalance of participation and so on. In the face of new transformations in city diplomacy，it is suggested that Beijing should deepen exchanges with international friendly cities，expand its influence in the international city network，take the initiative to set green recovery agenda，and pay attention to the effects of external publicity.