Abstract: As an important factor in pipeline design, sound pipeline toughness design can guarantee safe and reliable operation and delay or avert fractures. The focuses of attention for pipeline toughness design are safety and e-conomic rationality. With these two factors synthesized, the following basic principles for pipeline toughness design are presented on the basis of fracture mechanics: the principles of fracture control, fracture propaga-tion arresting and fracture pattern. Fracture control principle means to decide upon the requirements of pipe toughness design for fracture conyol according to the curve of Cv vs. critical pipe thickness; Fracture propagation arresting principle is that according to the CVN method which can predict toughness fracture and which was presented by W. A. Maxey, the strength, the higher the working pressure and the larger the pipe diameter, the higher the toughness required. The fracture pattern principle points out that, according to the relation between tearing rate and fracture shear area (S_A), the design and evaluation criterion for pipe toughness shall be 80%-85% FATT of the DWTT. The following factors having effect on pipe toughness are analysed: line pipe strength and design level, pipe thickness and diameter, medium transported, locations in pipe environmental impact, etc.