GPS has been used in positioning and navigation for decades. However, there are still many unsolved problems existing, for instance the degradation of positioning precision when the view of sky is obstructed. Pseudolite, a ground-based GPS satellite-like signal transmitter, can provide extra measurements in order to improve the positioning precision from GPS alone in the obstructed areas. In this study, pseudolite data were collected to tackle the obstruction of GPS satellite signals, and to evaluate the effectiveness of the GPS pseudolite. The results of this study demonstrated that the pseudolite observations reduced the effect of dilution of precision (DOP) by more than 35% and positioning precision by 40%, and with the addition of extra measurements it made 1cm positioning possible even in the obstructed areas.