The China Seismo-ionospheric Ground-based Monitoring Network in Northern China was established in August 2009, consisting of 5 vertical sounding stations and 20 oblique receiving stations. We analyzed the critical frequency of the F2 region (foF2) derived from vertical and oblique sounding data in this study. Our comparison results indicated that foF2 from vertical and oblique sounding presented very similar annual and semi-annual variation characteristics and along with the change in F10.7, the two data both enhanced after 2011. We calculated the root-mean-square error (RMSE), percent deviation (PD), and correlation coefficient (ρ) between the two data, which showed good positive correlation in Beijing, Changchun, Suzhou station. Our results also demonstrated that the consistency of vertical and oblique foF2 was better in the summer and equinox than in winter. The correlation on calm days for all stations was better than that in the magnetic disturbance period. Our research reveals that oblique sounding data presents similar change characteristics with vertical sounding data, thus these data can be used to investigate ionospheric phenomena.