In case of treating oil-contaminated soil which contains much water with thermal desorption process, any dry pre-treatment is necessary. There are some dry pretreatments such as hot air dry, microwave and direct heating. Among these treatments, microwave process spends a little time and cost compared to the other processes. To decide the optimal condition of microwave in this study, we analyzed TPH removal efficiency according to the height of the soil on the conveyer belt and the power degree of microwave while drying the soil with microwave. We set the height of the soil to 1cm, 2cm and 3cm to examine it, and did the strength of microwave to 2kW, 4kW and 6kW to do it. In case of 2kW microwave scanning, contamination removal rate of the soil showed little difference according to the height of the soil, in case of 4kW, the removal rate showed 72% at the soil of 1cm; 68% at 1cm and 58% at 3cm. In the examination according to the power of 6kW, TPH removal rate showed about 80% at 1cm of the soil; 70% at 2cm and 3cm from the test result, in respect of TPH removal efficiency, it was most efficient at the power of 6kW and the soil of 1cm height. However, when we considered the amount of energy consumption, the cost and the amount of the contaminated soil treatment from any efficiency almost same for each case, the optimal operating condition showed the optimal condition at the power of 4kW and the soil of 2cm height.