Cost-effective catalysts for electrocatalytic water splitting play a key role in the renewable energy research. Although Pt has been regarded as the best catalyst, its wide applications have been impeded by its high cost and scarce natural abundance. Therefore, decreasing the Pt usage for electrocatalyst design is significant toward the hydrogen evolution reaction (HER). Herein, flower-like Pt nanocrystals were loaded on the surface of nitrogen-doped graphene using Si nanowires as the sacrificial template. The experimental results showed that the optimal Pt nanocrystals/N-doped graphene with superior HER activity and excellent stability only has a low Pt loading of 5.0 wt%. It is noted that the HER mass activity of the Pt nanocrystals/N-doped graphene is 5 fold higher than that of the 20.0 wt% Pt/C commercial catalyst. This optimal catalyst also achieved a low Tafel slope (28.0 mV dec-1), large apparent exchange current density (0.989 mA cm-2) and high turnover frequency (2.05 s-1). This work may provide an effective avenue for developing highly efficient electrochemical catalysts for the HER.