Abstract: Reference database is inevitable problem in the research of gravity gradient aided navigation system (GGANS). Since complete gravity gradient measurement still needs a long time, gravity gradient approximation using theoretical methods has become a new way to build the reference map. In order to avoid some disadvantages, such as little consideration of existing gravity database, lack of physical meaning of modeled results in present researches, a reference map composition method starting from Free-air anomaly and Bouguer anomaly data is proposed in the paper. On the biases of gravity reduction, the principle of the mapping method is derived, and key algorithms in the computation also introduced. We present critical program flow when the method implement, and then make a detailed analysis on the effect of the method through two application examples. The result shows that most value and characteristics of the acquired reference map agrees well with measured gravity gradient data when high resolution gravity anomaly appears, which embodies practical value of the method. The method and correlative software work above can be referenced for the study of GGANS.