Detection of atomicity bug is valuable for analysing the concurrent errors of multi-thread programs development. The main ?difficulty? of the detection lies on how to recognise the execution sequence leading to program error from the cases of atomicity violations. To address this problem, we adopt a method of extracting atomic transition pairs by training test and a method of model detection, and present a new method named MC-AVIO which is an automatic atomicity bug detection method. Moreover, we implement a detecting tool AtomFinder for atomicity bug based on MC-AVIO. After testing several groups of open source software, it is proved that MC-AVIO is efficient in detecting ?atomicity? bugs.