The software delayed coincidence counting technology was researched based on embedded system. The device based on ARM processor was constructed to record time serials information of nuclear pulse. According to the different half-lifes of Po short-life daughters of radon isotopes, a method of software delayed coincidence count- ing was used to discriminate radon isotopes. Experiment results of ^220Rn and ^219Rn standard source measurement show that the software del od is practical for discrimination measurement of low 1 The software method is an alternative to hardware one, ience and flexibilit...