Currently, the traffic light signal controlsystem in Bangkok area applies the automationtechnology in order to control the flow of thetraffic. However, this automatic system does notcover every area in Bangkok in that only few arecovered. Most of the uncovered part area, it iscontrolled by human decision and the decision ismainly depended on the traffic police’s experienceand judgment. The control system still lacks ofefficient tool for supporting decision. The researchhas the objective to apply the engineeringknowledge and technique to develop effective wayfor solving the traffic jam problem in the short run apply urgently with low cost. The simulationmodel of traffic light control system is constructedwith Arena simulation package. The model is usedfor determining the efficient turn on – turn off lacktime in order that the flow of the car through thejunction road is maximized. The researchers selectto study the traffic situation on the Thaphra –Ratchada (Rama 3 road) during 7.00 am. - 9.00 am.according to the high accumulation of cars in thisarea and during this time. The experimental resultsand analysis from simulation experiment shows thatto control the signal with suggested output obtainedby simulation can improve the efficiency of carflow compared to the current situation withapproximately 28.67 %