Abstract: The purpose, significance, scope and methods of developing the reliability based management for large-scalecomplicated oil and gas pipeline network systems in China are preliminarily discussed. The methodology to deal with the practical issue of the life cycle phase of pipeline, including the stages of the pipeline pre-planning, design, construction and operation is presented. First, by introducing three variables (pressure, mass flow and temperature), the "working condition"and "functional status" of the pipeline network system within a certain range are described. Hence the calculation method for system reliability function under the expandable limit condition is proposed. A distributed and stepped mathematic model for reliability function is established and both safe transportation of oil and gas pipeline network and stable supply to the markets are taken into consideration. The model allows consistently the quantitative analysis and evaluation of the system reliability.