Metal selenides showing high theoretical capacity are promising for potassium-ion batteries, although their development is severely obstructed by their large volume changes and sluggish K-ion diffusion kinetics. Herein, it is found that the performance of NiSe anode materials could be boosted by a flexibly designed three-dimensional structure (denoted as NiSe@C/rGO), in which nano-sized NiSe shortens the ion diffusion distance, the amorphous carbon coating accommodates volume changes and prevents the electrode from side reactions, and rGO further enhances electronic conductivity and maintains structural integrity. Consequently, the NiSe@C/rGO anode exhibits superior rate capability (160 mA h g(-1) at 10 A g(-1)) and excellent cycling performance (301 mA h g(-1) after 700 cycles at 0.2 A g(-1)). Ex situ XRD and HRTEM observations reveal the reversible conversion reaction mechanism for K storage in NiSe@C/rGO. Qualitative and quantitative analyses by CV measurements indicate that the superior electrochemical performance also comes from the high contribution of pseudocapacitance.