The continuous frying experiment was proceeded at the frying temperature of 190 ℃for 32 h by using coil oil to fry dough sticks. The quality indexes of coil oil sample were monitored for each two hours, and the quality changes of coil oil during frying dough sticks were studied. The study found that after continuous frying for 32 h, the colour (OD_{448 nm}) increased from 0.028 to 0.673, the acid value of coil oil in creased from 0.33 to 2.40 mg KOH/g, the carbonyl value increased from 7.78 meq/kg to 94.70 meq/kg, and the total polar components increased from 3.81% to 30.16%. Compared with GB 7102.1—2003, the carbonyl value exceeded the limited quantity of ≤50 meq/kg after frying for 18 h, which was stated in the standard, and the total polar components exceeded the limited quantity (≤27%) after frying for 28 h. With the carbonyl value as the judgment index, the frying life of corn oil should be about 18 h, while it should be 27 h with the total polar components as the judgment index. The continuous frying experiment should not exceed 18 h at the frying temperature of 190 ℃ by using coil oil to fry dough sticks.