Distance is always an important parameter of spatial interaction models in geography and influences the range and depth of many social and economic activities. There is a close and important linkage between traffic flow and distance. So the regularity of distance decay of traffic flow becomes the important research field of transportation geography and economic geography. Based on the review and comment on research progress of distance decay regularity of traffic flow in foreign countries and China, we narrated the studying data and city specimens applied in this paper, and introduced the primary modals of distance decay function, including exponent model, Pareto model, logarithm model, square exponent model and extraction exponent model. Then we simulated the five distance decay model applying inter-urban traffic flow in China, including road passengers flow, railway passengers flow and railway cargo flow, and aviation passengers flow. We discussed the several parameters of their simulating results including distance decay coefficient b, correlation coefficient R and test parameters (namely F and T), especially provided a comparative analysis. According to the analytical result and simulating parameter, we chose the optimal function model of distance decay of traffic flow, namely, Pareto model, and wrote the specific function formulations of the four traffic flow modals.  So we further analyzed the parameter difference of four distance decay models and their geographical implication, especially the relation between distance decay coefficient b and the application distance of four traffic flow modals, and their changes about distance decay parameter of temporal inter-urban railway passengers and cargoes flow and their spatial explanation. To provide a further explanation, it is necessary to do so through analyzing the traffic flows and related social-economic index. So we protracted the accumulative ratio curves and distribution ratio curves of four traffic flows, and demonstrated the distance decay model of traffic flow, their parameter and decay regularity which provided an experiential discussion.