Recently, platinum-containing core-shell structures with tunable magnetic and catalytic properties have attracted intensive attentions and offered a wide range of applications. To date, their synthetic routes are mostly based on galvanic replacement, co-reduction, thermal decomposition and seed-mediated method. But the detailed formation mechanisms of core-shell structures in solution, especially, at gas-liquid interface are still not completely clear, which is mostly achieved based on post reaction studies or ex situ characterizations. In this regard, it is worthwhile but still very challenging to directly visualize the complicated and delicate dynamic processes.