Abstract: Ionosphere delay is the dominant error source of single frequency GPS ground deformation monitoring point coordinate precision, how to reduce the error source influence is the key point to enhance the precision of single and dual frequency mixed ground deformation monitoring system. Based on the data of Guangzhou Nansha single and dual frequency mixed GPS ground deformation monitoring network, analysis indicates that ionosphere delay influence is still large, even though the baseline length is short in low latitude region. The impact of ionosphere delay aggravates as baseline length increases, and the rule of seasonal change is quite obvious:significant in February, March, August and September. Dual frequency data is used to correct the ionosphere delay error in observation value domain, as a result, the precision is improved by 57%, indicating that the effect of observation domain correction is obvious.