IUU fishing hinders the effective management and conservation of fishery resources. Combating IUU fishing should make efforts in many links. Port state measures combat IUU fishing by eliminating or reducing the quantity of catches from IUU fishing.The Port State Measures Agreement provides a basis in international law for port state measures which came into force in 2016. This paper analyzes the main content of Port State Measures Agreement and the measures which have been adopted by some countries or RFMOs. On this basis, this paper analyzes the effectiveness and limitation of port state measures. As for the effectiveness, for example, port state measures can reduce the occurrence of IUU fishing and improve the possibility of finding IUU vessels; It also can make up for the defects of the flag state jurisdiction. As for the limitation, for example, it's difficult to implement port state measures in a short period of time because of inadeguate execution capacity of many countries; And it is difficult to confirm IUU fishing in the harbor because Port State Measures Agreement has not regulated the traceability information of catches. For China, port state measures can reduce the possibility of vessels which fly China's flag to engage in or support the IUU fishing. It'll perfect the oversight and control systems for fishing if China joins the Port State Measures Agreement. However, if China adopts the port state measures, China also will be faced with some challenges in the comprehensive reform of port supervision system and fishery supervision system and the construction of port state measures ability.