Many geoelectric resistivity observation stations have been disturbed by electromagnetic interference. In order to solve this problem,the Chinese scientists and technicians have made a lot of effort to a new observation system based on the AC power supply. The new observation system mainly consists of two parts:a low frequency transmit system and a reception system. The key technology of the transmitter system is analyzed in the paper. And we introduce the technology of SPWM and the research of high frequency voltage transformer. Finally,the transmitter system is tested in laboratory. The test results show that the transmitter provides a good output function and its specifications can meet the requirements.