Radio fingerprint databased (RFDB) is the prerequisite for WLAN based indoor positioning of the utmost importance. In this paper, a RFDB surveying method is proposed without dependence on additional information such as external hardware or indoor maps. In the method, the inertial data and the fingerprinting data are fused through graph optimization (GO). Then the indoor positions along with the RFDB can be estimated with greatest consistency of all types of information. The acquired RFDB can then be adopted for WLAN based indoor positioning. Experiments are carried out to evaluate the proposed method. It is proved that compared with pin point method, the proposed method has a mean positioning error decrease of about 1.0 m and compared with the Gaussian process based method with sparse reference points, the number is 0.8 m.