OBJECTIVE To measure and assess the levels of occupational exposure to power frequency electromagnetic fields in workers of power grid. METHODS PMM8053 electromagnetic fields measuring system with EHP-50 probe was used to measure the levels of electromagnetic fields at working place. Personal dosimeters (EMDEX LITE) were utilized to measure the individual exposure levels of power frequency magnetic field. The results were evaluated with the limitation criteria of GBZ2.2 and ICNIRP. RESULTS In the 500 kV ultra high voltage substation, the intensity at 90% measure points of power electric field was more than 5 kV/m. The magnetic field intensity in the areas nearby reactors and capacitors was often higher than 100 µT, even several hundreds µT. The mean daily exposure levels of workers in power grid were between 0.04 and 5.0 µT, and the exposure levels of 70% workers were higher than 0.4 µT. CONCLUSIONS In the areas of ultra high voltage and nearby the reactors and capacitors are the key control points for occupational health in power grid. There is acute health risk of workers exposed to high accumulative exposure levels.