The invention provides a mini-type multi-channel library construction instrument and a method for constructing a library, and specifically relates to the technical field of gene sequencing. The mini-type multi-channel library construction instrument comprises a rack, wherein the rack is provided with a first supporting plate and a controller; the first supporting plate is provided with a test tuberack for storing reagent strips and gun heads and a sample adding device; a waste liquid box is arranged at one side of the test tube rack; a heating device and a magnetic separation device are respectively and movably arranged at the bottom part of the test tube rack; the heating device and the magnetic separation device are respectively connected with a first transmission mechanism and a secondtransmission mechanism; the sample adding device is arranged above the test tube rack; the sample adding device is connected with a third transmission mechanism; the first transmission mechanism, thesecond transmission mechanism and the third transmission mechanism are electrically connected with the controller. According to the mini-type multi-channel library construction instrument provided bythe invention, the problems of time consumed for manually preparing a sample and low flux are completely solved; the whole process of a system is automatically completed by a one-stop working station, mistakes can be avoided, and the mini-type multi-channel library construction instrument is more suitable for standardization of a laboratory.