Abstract: BeiDou Navigation Satellite System (BDS)-3 has officially provided positioning, navigation and timing services to global users on July 31, 2020. Due to the differences in signal modulation modes and characteristics between BDS-2 and BDS-3, there will be inter-system bias (ISB) when the receiver receives and processes BDS-2 and BDS-3 signals. This paper adopts four random models: ignoring ISB(ISB $ _{NO} $), ISB estimation as constant(ISB $ _{CT} $), ISB estimation as random walk(ISB $ _{RW} $) and ISB estimation as white noise(ISB $ _{WN} $). GBM, WUM and CLK93 real-time precision products are used respectively. Based on the observation data of BRUX, CEDU, CUT0, HOB2, HARB and PTBB, the performance of mimic real-time and post precise point positioning (PPP) and time-frequency transfer of BDS-2/BDS-3 combination was evaluated. The results show that the average PPP positioning accuracy and convergence time of GBM and WUM products are both 1.7 cm and 23.3 min. The positioning and time-frequency transfer performance of the ISB estimation strategy is slightly better than that of the ignoring ISB strategy, and the data processing strategy of ISB $ _{CT} $ is the best. The 3D positioning accu-
Keywords: BeiDou Navigation Satellite System (BDS); inter-system bias (ISB); precise point positioning (PPP); positioning; time-frequency transfer