Abstract: Beidou navigation system is the only GNSS system in which all satellites can broadcast three-frequency signals.For the Beidou tri-frequency positioning performance, the author analyzes Beidou tri-frequency observation data quality and pseudo range single point positioning accuracy.Finally, based on the application of the engineering example, the positioning performance of Beidou tri-frequency is analyzed.The study found that the Beidou satellites in low latitudes have good visible and spatial distribution.The signal-to-noise ratio of B3 frequency is better than B1 and B2 frequencies, the multipath effect of frequency B3 is less than that of B1 and B2.Compared with the dual frequency combination, the positioning accuracy of B1/B2/B3 tri-frequency combination is greatly improved.In the practical application of the project, Beidou tri-frequency positioning accuracy is higher, the deformation information obtained is more accurate.The results provide a reliable technical support for China's natural resources survey and other basic surveying and mapping work.