With the unfolding of the Internet age and advertisements thriving on the Internet, the huge amounts of online advertisements and the emergence of the online advertising platforms brought severe challenges to the previous advertisement law. In response to the challenges, the advertisement law has been revised. One of the most important modifications is the introduction of a new online advertisement subject-the Internet information service providers（IISP）. Compared to the previous studies, this article conducts a systematic analysis on the legal nature and obligation model of IISP specified in the new advertisement law. IISP provides the third party platform services of making online advertisements. From the perspective of law, IISP is a type of Internet service provider (ISP). The new advertisement law stipulates the legal obligations of IISP and clarifies their obligation model as ″stop everything illegal if known or should be known,″ which is a third party obligation defined by the administrative law and which is not new in the Internet regulation. However, the obligation model in the new advertisement law is different from the usual models that were featured in the early stage with the process of ″detecting unlawful act-curbing-reporting″ and that were developed into ″monitoring(inspecting)-detecting unlawful act-curbing-reporting.″ The obligation model in the new advertisement law uses the expression ″clearly know or should know″ stemming from civil law instead of using administrative obligation wording ″detect.″ The implication of ″clearly know or should know″ in the new advertisement law, ″should know″ means that IISP is not liable for examination in terms of administrative law but liable for reasonable attention. This article particularly emphasizes the difference between examination obligation and attention obligation and clears up some misunderstandings about it. Examination obligation requires IISP to take active and initiative action to examine the content on the platform in detail and adopt necessary curb measures in a timely manner upon any discovery of unlawful act. In contrast, attention obligation does not require IISP to examine in detail, but to take necessary measures in a timely manner, or take certain technical precautions, such as technical filtering mechanisms, to prevent illegal content on the platform. Therefore, the attention obligation of IISP requires that IISP take technical measures to identify and control illegal advertisement content and take necessary measures to curb obviously illegal content. As to ″curb″, different IISPs can take different necessary measures and should take proper necessary measures based on their roles in the advertisement issuing process.