The regulatory requirement in Economic Commission for Europe (ECE R58) regulation applies to the Rear underrun protection devices which are intended to be fitted to commercial vehicles of N categories. The purpose of this regulation is to offer effective protection against underrunning of vehicles. This paper describes Computer aided engineering (CAE) methodology for testing rear underrun protection devices with loading sequences to be decided by Original equipment manufacturer. A sample model is prepared and analyzed to represent actual test conditions. Constraints and boundary conditions are applied as per test of vehicle. Finite element simulation is carried out using LS DYNA solver. Structural strength and integrity of Rear under protection device assembly is observed for different regulatory load requirement.