Abstract: The ionospheric observables can be determined by combining dual-frequency observations of GNSS through carrier-to-code leveling process, which mainly include the slant Total Electron Content (sTEC), satellite-receiver’s Differential Code Bias (DCB) and can be applied for ionosphere related research. However, the “leveled carrier phase ionospheric observable” is prone to be influenced by the arc length for leveling and receiver-dependent errors. In this contribution, an approach of calibrating sTEC and satellite-receiver’s DCB with ionospheric observables estimated with uncombined Precise Point Positioning (PPP) is proposed. With a short-baseline experiment, the sTEC determined with both kinds of ionospheric observations from one receiver were used to correct the corresponding observations of another receiver and single frequency PPP was implemented, the positioning results indicated a better reliability of sTEC calibrated with PPP-based ionospheric observables. Furthermore, by choosing a total of 4 days’ observations from 8 global-distributed IGS tracking stations (i.e. 4 days of Jan. 2009), all the satellites’ DCB are solved and compared with the products published by CODE, a discrepancy of no more than 0.1 ns can be found for PPP-based ionosheric observables in comparison of 0.2~0.3 ns for leveled carrier phase ionospheric observables, thus facilitate the precise study of ionosphere.