Abstract: The construction of the third-generation of Chinese BeiDou navigation system (BDS-3) was officially completed the construction on July 31, 2020. The BDS-3 provided new signals, B1C and B2a. Combining with B1I, B2I, and B3I signals from the second-generation of Chinese BeiDou novigation system (BDS-2), the article formed seven ionosphere-free combinations between different frequency to conduct dual frequency Precise Point Positioning (PPP) research. Results show that the positioning accuracy of all PPP combinations is on the order of centimeters.