Abstract: The obligations in public law do not belong to the concept of "obligation" we use in common sense, which means someone under obligation in private law to perform an act. Typical obligations consist of the obligation of contract, obligation of management under no duty, obligation of unjust enrichment and obligation of torts. Other kinds of obligations are un-typical obligations. Untypical obligations exist in the Civil Law widely, one of which is the reward request right of lost property finders. Compared with typical obligation, un-typical obligation is dependent, individual and scattered. Though the classification of typical obligations and un-typical obligations support the existence of General Provisions of the Obligation Law, there are problems in the classification. The classification of independent obligations and dependent obligations is better than the classification of typical obligations and un-typical obligations.