Gas replacement device is the key component of MAP machine. A new gas replacement device was designed and its structure and working principle was analyzed. The main parts' parameters of the new type MAP machine were calculated and analyzed. The performances of the new device were compared with that of the traditional device. The results showed that the structure of the new device is reasonable and compact; the gas exchange rate is 99.7%, while of that of the traditional device is 97%; the production efficiency is 280~300 packets per hour(double location), and the gas consumption reduces 0.33 kg/100 boxes. The performance of the new device has reached the anticipated goal.