We investigated the migration behavior of rodlike double-stranded DNA (dsDNA) in polymer gels and polymer solutions. Tetra-PEG gel, which has a homogeneous network structure, was utilized as a model system, allowing us to systematically tune the polymer volume fraction and molecular weight of network strand. Although we examined the applicability of the existing models, all the models failed to predict the migration behavior. Thus, we proposed a new model based on the Ogston model, which well explained the experimental data of polymer solutions and gels. The polymer volume fraction determined the maximum mobility, while the network strand governed the size sieving effect. From these results, we conclude that the polymer network with lower polymer volume fraction and smaller network strand is better in terms of size separation. The homogeneous polymer network is vital for understanding of particles’ dynamics in polymer network and a promising material for high-performance size separation.