The TIANSeq DirectFast Library Kit (MGI) is a DNA library construction kit specially optimized for MGI high-throughput sequencing Platforms. The kit is designed to perform DNA fragmentation, end repair and 3'-end dA-tailing in one step within a single tube. The product after this step can be directly used for adapter ligation without additional purification step. In addition, the PCR amplification reagent in this kit has been specially optimized to ensure high yield, good fidelity and no base preference for the amplified DNA library. The one-step streamline workflow of this kit skips multiple purification steps, and make sure the entire library construction process can be performed in 2.5 hr. This kit can achieve higher library construction efficiency, and can ensure the high efficiency of library construction for low input DNA samples.