Abstract: This paper presents a new method for single-frequency precise point positioning using code and phase measurement. Ionospheric delay in each code and phase measurement is estimated as unknown parameters together with receiver clock offset, tropospheric zenith path delay, receiver position and ambiguity of carrierphase. Modified square root information Filtering & Smoothing algorithm with parameter elimination is employed for parameter estimation. The proposed method can be applied to real-time positioning and post processing, and it is independent of any ionospheric model. With the presented method, static positioning test was carried out with data collected at 32 stations of the International GNSS Service (IGS) through day 75 to 90 in 2011,which show RMS in ENU are 0.023m，0.018m and 0. 059m respectively. Kinematic experiment with airborne GPS data collected on September 5th 2008 show that RMS in ENU compared with kinematic relative differential solution are 0.168m,0.151m and 0.172m.