In the study, the development of aerial platform truck of 42m boom system has been completed to be satisfied with working in much higher place. To avoid the rollover accident of vehicles while working, 3D FEA is applied to verify the 3D design, stress concentration, stress distribution, deflection, natural frequencies etc. In these analyses, traction load of Boom System, 700 Kg and traction degree analyzed to 0° ~ 85°. Analysis result, when Boom System's angle is 0°, could know that stress concentration and deflection are obtained to maximum. We could predict that maximum point of Stress concentration is 3.275 as safety factor and deflection of Boom system end part is max. 78.5Cm. Also could know that natural frequency and mode shape of boom system are stable in correlation with aerial platform truck's operation area. With these results, the structural stability of boom system in 42m aerial platform truck is obtained, then finally trying to find an optimum design of aerial platform truck.