This application provides a method for constructing a motion information list in video encoding and decoding, an apparatus, and a device, relating to the field of video encoding and decoding technologies. The method includes: obtaining candidate motion information and a length of the motion information list; based on the length of the motion information list, determining target motion information to check for duplicates in the motion information list; checking the motion information list to for duplicates by comparing the target motion information with the motion information list; and updating the motion information list based on whether the motion information list has a duplicate of the target motion information.