Variations of ionospheric TEC in the low latitude are investigated with the measurements of the dual-frequency GPS receiver in Hainan (19.5°N,109.1°E; Geomagnetic ordinates: 178.95°E,8.1°N) during 2005-2010.They are also compared with the ionogram-derived total electron content (ITEC) obtained with DPS4 digisonde in the same location and the International Reference Ionosphere model (IRI-2007) predictions (IRI-TEC) with different topside ionosphere options.Results show that (1) GPS-TEC has obvious diurnal and seasonal variations with a peak value at about 1500 LT and higher values in equinox than in summer and winter; the total electron contents produced by all techniques (GPS-TEC,ITEC and IRI-TEC) have similar variation trends; (2) there are systematically differences between ITEC and GPS-TEC; generally,ITEC is smaller/bigger than GPS-TEC during nighttime/daytime; there are smaller differences during nighttime and bigger ones during daytime,smaller differences in winter and bigger ones in other seasons which are different for the different year; (3) there is good linear relationship between ITEC and GPS-TEC; but it seems that GPS-TEC is saturated when ITEC is more than 60 TECUs; (4) generally the IRI predictions with old topside ionosphere option greatly overestimate both ITEC and GPS-TEC values and the IRI predictions with NeQuick topside ionosphere option are good agreement with the GPS-TEC and ITEC; (5) the differences between ITEC and GPS-TEC decrease from 2005 to 2010; but the differences between IRI-TEC and ITEC/GPS-TEC increase from 2005 to 2010.