Objective To survey dynamically the density of vector Aedes in the core area, warning area, and observing area, to evaluate the risk of dengue transmission based on the surveillance results, and to adopt control measures against vector Aedes. Methods From late August to late October, 2018, urban residential areas, rural residential areas, and nurseries or medical institutions were selected as surveillance habitats, and the densities of Aedes larvae in the observing area were surveyed by Breteau index (BI) every ten days; in the core area and warning area, communities with dengue cases received grid management, and the densities of vector Aedes were carried out emergency surveillance by BI and double bed net trap. Results The mean BI of observing area was 23.06. The mean BI varied widely in different counties (cities or districts). Ninghai county had the highest BI of 50.42, whereas Haishu district had the lowest BI of 4.81. The mean BI of urban areas (13.57) was significantly lower than that of suburban areas (33.84). By late October, the mean BI of the whole city declined to 14.09, especially in Haishu district (1.77) and Jiangbei district (3.54) (below the safety threshold, BI<5). The mean BI and bed net trap index in the core area and warning area were 3.27 and 1.02 mosquitoes per net per hour, respectively. Both BI and bed net trap index quickly declined and then leveled off after emergency investigation and settlement, and were below the safety thresholds after 2.61 and 1.57 days. Conclusion Based on the reasonable emergency surveillance of vector, combined with powerful prevention and control measures, the densities of dengue vectors can be effectively reduced to control the risk of dengue transmission.