Abstract: Subword-parallel adder can efficiently improve the performance of multimedia application.Based on the gate-delay model，this paper analyzes the design and performance of those scalar adders and presents two control mechanisms for subword-parallel：Carry truncation and carry elimination.Under the guidance of those two mechanisms，this paper implements several different subword-parallel adders and analyzes their performances.The results show that the carry elimination mechanism has shorter delay，fewer gates and lower power consumption than carry truncation mechanism.Among those subword-parallel adders，Kogge-Stone adder has the shortest delay and ripple carry adder has the fewest gates and lowest power.The research results presented in this paper can be used to guide the design and selection of subword-parallel adders.