Abstract: Ca is widely abundant in nature and its rodioisotope 41Ca is a cosmogenic nuclide with a half－life of 10E5 years. However, the 41Ca/40Ca ratio in natural samples is very low and can only be measured by accelerator mass spectrometry(AMS). The application of 41Ca is very important not only in the life science but also in geological dating, global environment change studies and astrophysics. The measurement of 41Ca with AMS and its applications are reviewed, with particular mention of the research in the China Institute of Atomic Energy.