Nitriding is a process that brings to the surface of the steel parts, especially tool steel ones, valuable properties such as: high hardness (up to 70HRC), excellent resistance to wear, corrosion and fatigue, thereby improving their service life. The nitriding process is carried out nomally at the low temperature range, therefore to achieve nitriding layers with the thickness of hundreds of microns, the nitriding time needs to be very long resulting in high cost. Accelerating of the nitriding process is the aim of many research work to shorten the process while still maintains the quality of the nitriding layer on the tool steel. This paper studies the influence of the presence of intermediate layer on the microstructure and properties of the nitriding layer. Then, appropriate pre-treatment method for SKD11 tool steel will be investigated.