The invention provides a device and a method for predicting a motion vector and belongs to the technical field of digital video encoding and decoding. By using a front time domain motion vector predicting module and a back time domain motion vector predicting module and by controlling serial execution of each predicting mode, resources of a computing unit, particularly resources of a multiplier and a divider, are greatly saved. A macro block pipeline structure uses a zig-zag macro block scanning structure. By the structure, the problems that during pipeline work, the motion vector prediction depends data are solved, the prediction can be carried out in parallel, encoding performance is improved, and complexity of the encoding system is reduced. By an initialized module of a neighbor block and an initialized module of a current block, complex data update during the motion vector evaluation is converted into a simple data table. By a table searching mode, control is simplified, encoding complexity is reduced, working clock is saved, and requirement on real time of high-resolution video encoding is met.