Objective To investigate the species composition, density, and seasonal variation of vectors in Gansu province, China, and to provide a scientific basis for vector prevention and control in this area. Methods According to the National Vector Surveillance Implementation Plan, the rodents, mosquitoes, flies and cockroaches were monitored at the vector surveillance sites in Gansu province in 2018. The trap-at-night/night-cage method, lamp trapping method, spoon method, cage trapping method and sticky trap method were used to survey rodents, adult mosquitoes, larval mosquitoes, flies and cockroaches, respectively. Excel 2010 software was used to analyze the surveillance data. Results The overall capture rate of rodents was 0.63%; Mus musculus was the dominant species, accounting for 72.31% of the total; the peak period was November. The overall density of adult mosquitoes was 11.94 mosquitoes/lamp·night; Culex pipiens pallens was the dominant species, accounting for 77.84% of the total. The positive dip index of larval mosquitoes was 7.79%, with the highest ratio (92.25%) observed in the larvae of Culex; the peak density was in July for both adult and larval mosquitoes. The overall density of flies was 2.78 flies/cage; the peak density (5.69 flies/cage) was in July. The overall density of cockroaches was 0.47 cockroach/cage, with an infestation rate of 8.71%. All the cockroaches captured were Blattella germanica, with their peak density in May. Conclusion Mus musculus was still the dominant rodent species in Gansu province. The dominant mosquito species was mainly Cx. pipiens pallens, but the constituent ratio of Cx. tritaeniorhynchus has significantly increased compared with that of the previous year. The peak density of flies was observed in July. The density and infestation rate of cockroaches have decreased to some degree as compared with those of the previous year; all the cockroaches captured were still German cockroaches. Prevention and control measures against Japanese encephalitis should be strengthened.