The exposure to electric field now-a-days is an integral part in the design area of electrical power apparatus and systems. Moreover the electric field produced by power lines, busbars and all high voltage equipments inside high voltage (HV) substations is receiving more and more concerns to guarantee the safety of workers inside these substations. Therefore monitoring the electric field inside air insulated substation (AIS) is achieved in this paper. In this paper not only the simulation of the electric field using charge simulation method (CSM) in three dimensional (3D) is achieved by using electric field modeling program developed by the authors but also the electric field is measured into actual conventional 500/220 kV Cairo 500 substation under 500 kV bus-system. The simulated results are compared with the actual measured values. The simulation results are matched with the measured values with a very small tolerance about 4.4%.