Abstract: Objectives: The Observable-specific Signal Bias (OSB) provides a simple and unified way for phase/pseudo-range bias correction in multi-frequency and multi-constellation GNSS data processing. The quality of real-time OSB products directly affects the performance of Real Time Precise Point Positioning with Ambiguity Resolution (RT PPP-AR). The Centre National d'Etudes Spatiales (CNES) is currently the only research institution that publicly releases real-time OSB products which promote the practical applications of multi-frequency and multi-constellation RT PPP-AR. This study first evaluate and analyze the quality of real-time OSB products from CNES and their impact on RT PPP-AR solution, aiming to provide a reference for increasing RT PPP users. Method: After evaluating the availability and stability of real-time OSB Products from CNES, the ambiguity residual distribution situation were statistically analyzed. Simulated kinematic and static positioning experiment were carried out to verify the positioning performance of RT PPP-AR based on real-time OSB Products from CNES for several different system combinations. Results: Experimental results show that real-time OSB products from CNES demonstrate high availability, good stability and high accuracy. As for the availability of phase/pseudo-range OSB products for GPS/Galileo/BDS systems reaches over 90%, but for some satellites (such as G28, E02, E07, E21), the availability ranges from 40% to 80%. The stability of GPS/Galileophase OSB products is better than 0.1 cycles, while that of BDS is slightly lower. The daily average standard deviations (STD) for GPS/Galileo/BDS systems is 0.085, 0.117, and 0.228 cycles, respectively. After applying OSB corrections, the residual ambiguity for wide-lane (WL) and narrow-lane (NL) of GPS/Galileo/BDS satellites is small, with percentages within ±0.25 cycles as follows: 92.4%, 95.9%, 86.6% for WL, and 88.4%, 91.5%, 87.4% for NL, which satisfies the requirements for ambiguity fixing in PPP. The real-time PPP-AR positioning accuracy using OSB products from CNES is validated with MultiGNSS Experiment (MGEX) observations. The results show that RT PPP-AR using real-time OSB products from CNES can achieve centimeter-level positioning accuracy in dynamic mode. The positioning errors in the east, north, and up directions for GPS+Galileo+BDS RT PPP-AR are 1.16 cm, 0.95 cm, and 2.78 cm, respectively. Compared to float PPP results without OSB correction, RT PPP-AR significantly reduces the convergence time by more than 40%. Conclusion: Ambiguity resolution can be achieved under BDS single system based on real-time OSB products from CNES. And the positioning accuracy is significantly improved compared to float solution, while the fixing rate is around 94%.