Existing methods for trajectory privacy-preserve can't protect K-anonymous protection from attacks with background know ledge. To this end,a method generating dummy trajectories with user's true trajectories is proposed. By generating( K-1) dummy trajectories to achieve K-anonymous with true trajectories,adversaries can't identify them through randomness. By modeling the Markov model of user 's trajectories with considering background information,dummy trajectories can 't be broken because of background inf...