Abstract: POD (Precision orbit determination) of Mars exploration spacecraft is vital to its mission and scientific objects implementation. Besides using for POD, Martian gravity field is an important constraint for researches about Mars internal structure, Mars surface mass transformation and Mars origin and revolutionary. Considering the importance of Mars spacecraft POD and Martian gravity field, POD of MGS (Mars Global Surveyor) is done using nearly two months tracking data during mapping phase, and the accuracy of orbital result is evaluated by orbital overlap analysis. In following Martian gravity field model is solved, and the model accuracy is assessed by methods such as gravity power spectrum, orbital residuals and Mars free-air gravity anomaly, the results show the reasonability of the solution, and dominating Martian gravity field information can be extracted by nearly two months tracking data. The work lays foundation for application of our national Mars exploration mission “YH-1” tracking data in Martian gravity field research..