Abstract: The business characteristics and water area division are described about maritime traffic safety supervision and administration. Based on the factors of vessel traffic flow, danger and accidents, the risk assessment index system is put forward about the water subarea. The risk adjustment factors are proposed from the port function level in the water subarea. With the index comparison, normalization treatment and analytic hierarchy process, the measurement methods are issued about the single risk and comprehensive risk index. The research result is applied to the water subarea risk assessment and provides technical support for maritime traffic safety planning preparation and business development.