Accurate global radiation measured by pyranometer is very important for correcting radiation datasets observed by satellites, validating outputs of radiation transport model, climate change research, and quantitative evaluation of solar energy resources. Because most of pyranometers are made based the thermopile principle, the accuracy of global radiation measurement by pyranometers is impacted by all kinds of thermal noise inevitably. Namely there are thermal offsets in global radiation data observed by pyranometers. With the deepgoing of climate change researches in recent years, the accuracy requirement of ground measurements of the total solar radiation is higher. Many researchers at home and overseas have paid close attention to the researches on physical mechanisms and thermal offset correction methods of pyranometers. The following aspects are reviewed: (1) the discovery of thermal offsets of pyranometers; (2) progresses in characteristics and physical mechanisms of thermal offsets of pyranometers; (3) progresses in correction methods of thermal offsets. Appropriate comments about existing problems and research direction are given, and revelation about researches on physical mechanisms and thermal offset correction methods of homemade pyranometers are provided.