Abstract:First, based on the double-differenced positioning mathematical model and the VTEC temporal–spatial distribution of China region, we analyze the influence of higher-order ionospheric delay on L3 observation. Second, to investigate the temporal-spatial distribution characteristics of the higher-order ionospheric effect on GNSS double-differenced positioning in China region, GNSS data from 41 CMONOC stations spanning the year 2015 are processed based on the double-differenced positioning technology of BERNESE GNSS software version 5.2. Numerical results show that the influence of high-order ionospheric delay on double-differenced positioning in China region is related to the distribution of the selected stations, and there are obvious semi-annual variations and directional difference. With high latitude sites moving north and low latitude sites moving south, the size of the annual averages are up to 2 mm.