Abstract: The current quantitative analysis of GPS position errors using pseudoranges is still not accurate enough. Therefore, in this paper, GPS position errors in an east-north-up local topocentric coordinate system were further analysed in two scenarios. Firstly, using all visible satellites for positioning, the expressions of GPS position errors were modified by setting corresponding parameters for different latitudes. Secondly, four optimum satellites were selected for positioning, the expressions for GPS position errors were first derived for a more practical situation. On this basis, the interrelationships between various position errors were established for the above two scenarios, respectively. It was designed that, if the standard deviation of a user ’s pseudorange error <i<σ</i<<sub<URE</sub< was known, the standard deviations of GPS position errors could be estimated more accurately according to the proposed formulas. The accuracy of the proposed formulas was verified using a SPIRENT satellite signal simulator, generating realistic satellite signals at the equator,45° north latitude and the north pole respectively.