In existing procedural synthesis methods, manual terrain modeling is a laborious process, which is always difficult to adjust results. To solve these problems, an interactive method based on sketch map is proposed. Utilizing a user-drawn sketch map to exactly control the placement of terrain features, and some control parameters to adjust details of synthesized terrain, the proposed method reaches a good balance between automation and controllability. Experiments show that terrain is synthesized efficiently, and the synthesis result can be controlled conveniently by the users, who may even lack of special modeling skills. To a certain extent, it accelerates the transition from manual to automated terrain modeling.