The mobility of Migrating Instance（MI） brings many risks to the migrating workflow system. Especially, the codes of MI face the risk of being maliciously manipulated by the hostile working places. This paper presents an initiative mechanism of safe-guarding the codes of MI based on danger theory: for MI consists of several modules in order to complete relative tasks, MI will detect whether the block MI determines to run changed before executing. If there are some changes, MI will then perceive whether the changes dangerous; if dangerous, appropriate measures will be taken to amend the damaged codes and then obfuscate them lest this module will be attacked easily again. This mechanism improves the efficiency of MI compared with other mechanism, and makes MI avoid temporary attacks, which are illustrated with the experimental results at the end of this paper.