The purposes of research are to show a way to analyze architectural/urban space and to consider a spatial design method. In architectural or urban space, there are infinite elements like people, buildings, trees, and so on. They interact constantly with each other and the composition is changing perpetually. So in this study, architectural/urban space is understood as a discrete system, where all the elements continuously interact and change in discrete time. The system is analyzed focusing on the human behavior, in order to understand the interrelation between people and architectural space. These 4 steps are followed; 1) Observation and description of human behaviors 2) Analysis of the description and extraction of main spatial behavioral rules 3) Spatial behavior modeling and simulations with Cellular Automaton based on the extracted rules 4) Consideration of a space design resulting from the comparison of the spatial characteristics of the simulated and the observed spaces.