With the increasing needs for high-performance gas sensors in industrial production, environmental monitoring and so on, the research on gas sensors is becoming more and more important. In this paper, the electric field intensity distribution simulation process of the interdigital microelectrodes (IMEs) is discussed in details to get the proper electrode structural parameters. The IMEs on the ITO surface with a minimum gap of about 4μm are achieved by lithography, which provides a reliable, low-cost manufacturing method. Sensitive components are made of the multi-walled carbon nanotubes modified materials. The gas-sensing property of the sensor is detected for ammonia. The experiment result shows that the performance of the nanomodified sensor is obviously improved.