Using the new inner surface modification technique named GEPSⅡ(grid-enhanced pl asma source ion implantation), which is designed for inner surface modification of tubular work piece, has successfully produced TiN coating on 0.45% C steel (4 5# steel). By comparing with the uncoated 45# steel sample, the electrochemical corrosion test on the coated 45# steel samples presents about 5—10 times improv ement in their corrosion resistance. Structural analysis shows that the TiN coat ings have preferred crystal orientation(111) and (2000). And the depth of coatin gs is about 20 nm, with part of which embedding in the substrate.