Graphite, as a typical carbon allotrope, is demonstrated as an available intercalation-type anode material for potassium-ion batteries (PIBs). The main challenges associated with graphite anodes are structural pulverization and instability of the solid electrolyte interphase (SEI) resulting from the repeated volume change during charge/discharge. In this work, a layer of interweaved carbon nanotubes (CNTs) are grown on the surface of micro-size graphite flakes through controllable in-situ catalytic chemical vapor deposition method (CCVD), and the CNTs content can be easily adjusted by varying the deposition time. The CNTs-interweaved layer can not only stabilize the graphite structure but also enhance the diffusion kinetics of K+ during cycling. Furthermore, CNTs also provide a certain amount of capacity. The composite material of in situ growing carbon nanotubes and modified graphite flakes (CNTs-MG) exhibit a reversible capacity of 234 mAh g−1 at 2 A g−1 after 1500 cycles, which is obviously better than that of counterpart graphite flakes. Besides, the K storage mechanism and the effect of the contents of CNTs are also investigated systemically by in-situ Raman spectra and electrochemical characterizations.