The experiments of ionizing radiation were performed on floating gate ROM device s by using 60Coγrays. The experimental aim was to examine the radi ation response at various dose rates. According to the extrapolation technique and the failu re criteria we defined,the parameter failure and function failure of devices vs. dose rate were studied. Finally, based on the function of failure timevs. doserate, the failure time of floating gate ROM device in space radiation environm ent was predicted.