Abstract: A digital design flow chart for tunnel drilling rigs is defined from the perspectives of small-lot customization and variation development firstly. Then three key technologies for the digital design of drilling rigs have been proposed, i.e, digital modelling, simulation and management. The first is used to support 3-D modelling and assembly analysis, the second is used to analyze the dynamic performance of drilling rig, and the third is to manage the design process and the data generated in it. A digital design platform has been subsequently developed, including the base layer, platform layer and application layer. Finally, a design case of one-kilometre directional drilling rig is given to demonstrate the application of digital design technologies.