Though the suggestions on health risk assessment of extremely low frequency (ELF) electric and magnetic fields (EMF) by WHO has gradually begun to spread relative effectively among the administrative departments of environmental protection in China, there are still individual media or experts calling for reducing exposure limits to the arbitrary low level in the name of precaution, and endeavoring to affect the government to make decisions or management policies on EMF, with the purpose for their own interest. It has been leading to the increasing anxiety and fear towards EMF of general public. Based on the current status of EMF issue and standard development in China, this paper analyzes the principles of precautionary policies and related precautionary measures on EMF worldwide in combination with the result of risk assessment on ELF EMF and the suggestions for standards on exposure limits by international organizations, and comprehensively considers the practical situation of power transmission and transformation projects to put forward the recommendations. The exposure limits provided in the guidelines or standards by international organizations, such as International Commission on Non-Ionizing Radiation Protection (ICNIRP) and Institute of Electrical and Electronic Engineers (IEEE), is safe enough to protect the health of general public. And for power transmission and transformation projects, the basic restrictions are the essential limits in these guidelines or standards, while the reference levels are just easier to implement in practical for guidance. The set of criteria for precautionary principle provided by European Union could be regarded as the reference for the development principle of precautionary policy, involving proportionality, non-discrimination, consistency, examination of the benefits and costs, examination of scientific developments and so on. Since in fact the EMF by power transmission and transformation projects belongs to weak risk, the core of precautionary policies lies in being no or low cost in practical, especially for new electrical equipments.