The improvement of the resolution of DNA sequencing by nanopore technology is very important for its real-life application. In this paper, we report our work on using molecular dynamics simulation to study the dependence of DNA sequencing on the translocation time of DNA through a graphene nanopore, using the single-strand DNA fragment translocation through graphene nanopores with diameters down to ∼2 nm as examples. We found that A, T, C, and G could be identified by the difference in the translocation time between different types of nucleotides through 2 nm graphene nanopores. In particular, the recognition of the graphene nanopore for different nucleotides can be greatly enhanced in a low electric field. Our study suggests that the recognition of a graphene nanopore by different nucleotides is the key factor for sequencing DNA by translocation time. Our study also indicates that the surface of a graphene nanopore can be modified to increase the recognition of nucleotides and to improve the resolution of DNA sequencing based on the DNA translocation time with a suitable electric field.