Since natural disaster risk is a feature of the future and is also dynamic, the result of probabilistic risk analysis for natural disaster has its own time limit. Considering that risk is for the future and meanwhile dynamic, the result of probabilistic risk analysis in natural disaster could just represent risk for a limited time, which is the timeliness of probabilistic risk. Besides, the length of the timeliness is just called the period of validity of probabilistic risk for natural disaster. Because the system of natural disaster risk is complex and comprehensive, the dynamics of natural disaster risk is caused by numerous reasons related to both natural and social environment and is with great uncertainty. Therefore, qualitative analysis could be a feasible method for the timeliness evaluation of probabilistic risk for natural disaster.