Abstract: The decision of TIA threshold is one of the most important problems. The authors analyze the present situation of the research about TIA threshold abroad, study China's city traffic characteristics, basic traffic research situation, land development and economic level, and establish for the first time the theory and method of TIA threshold which adapt to China's city characters. According to the volume of traffic produced by building item, the development type, intensity and location, etc, the threshold is divided into peak hour traffic, day traffic, total travel person-time in peak hour, development type and intensity, service level and the maximum travel threshold, etc. and the special method to decide all the thresholds is also put forward. At last taking the decision of TIA threshold of a certain area of Beijing for example, the authors express their viewpoints on threshold.