Diurnal variations of ionospheric F2 layer at Zhongshan (Jun.) and Tromso (Dec.) in winter are comparatively studied by analyzing the data from DSP-4 in 1996, 1997, 1998 and 2002. Combining the results of the numerical simulation, we analyzed the main physical processes which are responsible for the F region ionosphere over Zhongshan and Tromso. The results show that, although both Zhongshan and Tromso have similar geographic latitudes, the mechanisms of the foF2 diurnal variation are not always the same. As a result of the strong interaction between sunlit ionization and horizontal convection, the major peak in the diurnal variation of foF2 at Zhongshan appears around geomagnetic local noon, while the F region at Tromso is less influenced by the horizontal convection on the dayside, making the major peak in the foF2 diurnal variation at about local noon. The foF2 diurmal variations at the both stations are greatly influenced by solar radiation flux, and the auroral particle precipitation has a notable influence on the foF2 diurnal variation at Zhongshan station in solar minimum.