This research is an attempt to understand the distribution of axial loads on columns in one story building model under different case of slab (rigid and flexible slab) and different load condition (gravity and horizontal load), then comparing the results obtained by model with those results obtained by tributary area method. To do this, a technique utilizing finite element analysis is used in order to create computerized model with SAP2000 program. This model is built to simulate the real state of slab and columns in one story building. According to the analysis of the data obtained, we can see the big difference between the real load carried by columns and the load calculated by using the Tributary area method, so using 3-D model is the best method to calculate the real load effected on columns and design this columns according this load. Keywords: Tributary area method, rigid slab, flexible slab, FEM analysis, stiffness