Using a new inner surface modification method named GEPSⅡ (grid-enhanced plasma source ion implantation),which is designed for inner surface modification of tubular work pieces, we successfully produced polycrystalline TiN coating on 0.45% C steel (45# steel) samples. Compared with the uncoated 45# steel sample, the electrochemical corrosion test on the coated 45# steel samples presents evident improvement in their corrosion resistance. Two implanted voltages, direct current (-2kV) and pulsed negative voltage (-10kV), are applied on the substrates. It is shown that the direct current implantation is more effective than the pulsed implantation in the surface corrosion resistance. AES depth profile shows that coating thickness is about tens of nanometres. The preferred orientations expressed by peaks at (111) and (200) can be seen clearly in XRD pattes.