Abstract: In this paper, we use the Langmuir single probe and double probe to diagnose a low-temperature low-pressure isotropic plasma induced by microwave electron cyclotron resonance (ECR) device. The results show that the plasma density which calculated by ion saturation current is about 21010/cm3 and by electron saturation current is just about 11010/cm3 . The electron temperature which measured by Langmuir single probe is up to 7eV and measured by double probe is just up to 4.5eV in the axial. Langmuir orbital motion limited theory is introduced successfully to achieve separation of electron current and ion current. This paper solves the problem that the linear part of the single electron temperature probe reading is not obvious.