This work builds varied nanostructures on the boron-doped diamond (BDD) film by changing the surface status of the silicon (Si) substrate in a facile method and investigates the influence mechanism of surface morphology of the substrate on the capacitive performance of the formed Si/BDD electrode. The BDD electrodes with different nanostructures are synthesized by hot filament chemical vapor deposition (HFCVD) technique on the etched Si wafers, which are etched in HF (5 M)/AgNO3 (0.035 M) aqueous solution (55 degrees C) from 0 to 50 min. Results show that it forms surface structures and contents of doped boron atom and sp(2)-C bonds of BDD electrode on the Si substrates with etching time varied. The varying structures and compositions may induce changes in capacitive performance of the BDD electrode. In 0.1 M Na2SO4 aqueous solution, sample D at etching time of 30 min obtained the biggest capacitance of 103 mF/cm(2) at current density of 0.1 mA/cm(2). In particular, the capacitance is 27 times higher than that of sample A without etching. Sample D also has retention of 80% after 3000 cycles, indicating a dependable stability of the electrode. A mechanism is then proposed how surface morphology of Si substrate affects the capacitance properties of the Si/BDD electrode.