We propose the design of DMA controller for 32bits low power SOC system, which expedites transfer of unaligned data through onthefly reassembling bytes by hardware circuit, requiring fewer resources, power and no extra software overhead. Although user configures the transfer of unaligned data in byte format, the DMA controller can automatically reorganize bytes in proper way, so as to transfer data in word format correctly and faster. Verification shows the design can evidently improve transfer efficiency of unaligned data. The design method has been applied to a MCU chip for electricity information acquisition system, and assists software to deal with encryption and decryption, to form communication frames, etc. The results show that the DMA controller works with high efficiency while easy to use, so the design meets the requirements.