The research progresses of the gas sensors based on microfiber evanescent field effects are summarized. Meanwhile, the sensing principle and faced problems are explained. The research progresses of three kind structures gas sensors based on microfiber evanescent field effects, such as just depending on microfiber evanescent field effects, coating sensitive film on the microfiber surface, and combing with other optical microstructure, are focused. Although some research results have been achieved, many problems and challenges are facing. We believe that with developing of the research, owing to their unique performance advantages, the gas sensors based on the microfiber evanescent field effects are still possible to become a strong competitor for the existing gas sensors.