The behavior of styrene solution polymerizationat the initial state of reaction was studied byexperimental and program for investigate the start uptime and the rate of reaction. A new program wasdeveloped by experimental data for predict the start uptime and the rate of reaction. This program is designedto operate under the Window 95 operating system foreasily use. The developed program is included of the physicalproperties calculation unit the material balance unitand the start up calculation unit. The physicalproperties unit and the material balance are tested bycompare with the existing program. The comparisonresults were very close the existing program. For therate of reaction calculation results, at the differentcalculation step, it was found that the results weresimilar. For the start up time calculation results ofthe developed program were lower than the results ofthe existing program about 12.8 minutes or 4.39%. Inthe first 90 minutes period, the rate of reaction thatcalculated the developed program were +/- 30 %different from the existing program and the 90 minutesupper the results are higher than the existing programabout 6.00%