Among many indoor positioning methods, WiFi based indoor positioning has great potential use in location based Service (LBS) applications. A new WiFi based positioning method is proposed in this paper, which adopts the prior information of user walking patterns. The method can also effectively adopt the traditional hierarchical positioning structure. In the pre-coarse positioning phase, the method can adopt the position estimation from the previous time to define the potential areas. In the signal fingerprint test phase, the potential areas can be tested to know whether it is right or wrong. If wrong, the second coarse positioning phase is carried out to re-define the potential areas. Then in the fine positioning phase, the maximum posterior (MAP) based method is adopted to estimate the user position. The proposed method is tested using an open access dataset, the results have shown that the proposed method can effectively adopt prior information and can increase positioning accuracy by 3%, 5% and 7% over the traditional methods ( no prior&MAP, prior&kNN and no prior&kNN) respectively.