Abstract: Combined with VTEC Spherical Harmonic Function Model,the Kalman Filter with external constraint condition between some parameters solved is used for real time estimation of GPS satellite and receiver's Differential Code Bias (DCB). This can be used to provide DCBs for Wide Area Augmentation System's real time ionosphere delay modeling. The results show that the DCB can converge in short time in this solution. The final value of those DCBs is in little bias comparing with the results of IGS.