A motion estimation method includes: (A) defining one pixel in a reference image as a center of search (CS) corresponding to a target pixel set in a current image; (B) determining a center error (CE) signal; (C) defining another pixel in the reference image as a target of search (TS) with reference to the CS, one candidate search vector available for selection from a vector set, and a step size; (D) determining a target error (TE) signal; (E) determining whether to update the CS and the CE signal; (F) if determined, updating the CS, the CE signal and the vector set; (G) repeating steps (C)˜(F) using a candidate search vector selected from the vector set and the same step size until there is no candidate search vector available for selection in the vector set; (H) repeating steps (C)˜(G) using a smaller step size until a predetermined value is reached; and (I) computing a motion vector based on the target pixel set and one pixel set that includes the CS.