Abstract: The main purpose of the study was to test GPS equipment receivers used for open sky and forest condition with non differential and RBN differential mode, and to quantify satellite availability, PDOP, accuracy, and precision under different factors, the objective being to assist GPS's application in precision forestry. Results of stationary test showed that the RBN DGPS mode improved the accuracy and precision both in open sky and forest condition. Comparing to the open sky, forestry GPS application decreased the number of satellites availability by 2-3, increased PDOP by 0.8-1.2, reduced accuracy by 0.30-0.31 m, and reduced precision by 0.92-1.01 m. In mobile test, analysis of variance(ANOVA)with SPSS16.0 was used to clarify the effects of positioning mode and site condition on the precision of GPS. According to the ANOVA test, the GPS positioning perimeter and area were affected significantly by positioning mode, site condition and their interaction. Based on the research, it is clearly possible to obtain good accuracy of a RBN GPS in forest, and forest observational conditions made extremely different conditions for GPS observation owing to forestry canopy causing strong multipath effect and satellites signals reception.